Evaluation of the adult with nontraumatic abdominal or flank pain in the emergency department

INTRODUCTION — 

Abdominal and/or flank pain is the chief complaint in 5 to 10 percent of emergency department (ED) visits, and patients often require extensive evaluations, including testing, administration of analgesia, stabilization, and specialty consultation [1-5]. In many cases, the differential diagnosis is wide, ranging from benign to life-threatening conditions. Causes include medical, surgical, intra-abdominal, and extra-abdominal ailments. Associated symptoms often lack specificity, and atypical presentations of common diseases are frequent.

Despite sophisticated diagnostic modalities, undifferentiated abdominal pain remains the diagnosis for approximately 25 percent of patients discharged from the ED and between 35 and 41 percent for those admitted to the hospital [2,6-8]. Approximately 80 percent of patients discharged with undifferentiated abdominal pain improve or become pain free within two weeks of presentation [8].

Older adults, patients with immunocompromise or diabetes, and female patients of childbearing age pose special diagnostic challenges. Older adults and patients with diabetes are at greater risk for potentially life-threatening conditions and often present with nonspecific complaints and atypical symptoms [9,10].

This topic will discuss the evaluation of the adult patient presenting to the ED with nontraumatic abdominal or flank pain. The outpatient evaluation of adults with abdominal pain, a synopsis of causes of abdominal pain, an approach to pelvic pain, and evaluation of blunt abdominal trauma are found separately.

●(See "Evaluation of the adult with abdominal pain".)

●(See "Causes of abdominal pain in adults".)

●(See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients".)

●(See "Acute pelvic pain in nonpregnant adult females: Evaluation".)

●(See "Blunt abdominal trauma in adults: Initial evaluation and management".)

OVERVIEW OF THE EVALUATION

Rapid assessment for abdominal catastrophe — The evaluation of an adult emergency department (ED) patient with abdominal or flank pain starts with obtaining a history and performing a physical examination. We simultaneously and rapidly assess if the patient may be having a life-threatening abdominal catastrophe. Potential indicators include shock (eg, hypotension, tachycardia, tachypnea), presence of peritonitis, significant distress from pain, or altered mental status; these warrant starting resuscitation simultaneously with obtaining further history and examination. (See 'Patient with suspected life-threatening abdominal catastrophe' below.)

History — A thorough history focuses the differential diagnosis and helps determine the need for further testing. It is important to characterize the pain as precisely as possible, including timing of onset, continuous or intermittent pattern, prior episodes of similar pain, quality, location, radiation, aggravating and alleviating factors, and associated symptoms. Patient factors and clinical features of high-risk abdominal pain are presented in the table (table 1). High risk symptoms include acute onset, initial maximal severity, and pain preceding vomiting. Symptoms in older patients are less likely to be characteristic for the underlying cause of their pain (ie, "atypical" symptoms). (See 'Older adults' below.)

●Quality and timing of pain — The quality and timing of the pain (eg, intensity at onset, acute versus chronic) help determine the acuity and focus the evaluation on specific organ systems. Severe, sudden-onset pain or constant, worsening pain lasting over six hours (but less than 48 hours) suggests a surgical cause, while nonsurgical causes tend to have milder, intermittent pain with longer chronicity. Abdominal pain can be classified as visceral, parietal (ie, somatic), or referred depending on its neurologic basis, which is discussed in detail separately (table 2). (See "Causes of abdominal pain in adults", section on 'Pathophysiology of abdominal pain'.)

Pain intensity at onset provides clues to disease severity and involved structures [1,11,12]. Pain with maximum intensity at onset is concerning for a vascular process (eg, ruptured abdominal aortic aneurysm [AAA]), obstruction of a small tubular structure (eg, nephrolithiasis), or reproductive organ pathology (eg, ovarian cyst rupture or torsion) [13]. Intense tearing pain suggests aortic dissection or rupture. Pain with gradual onset suggests an inflammatory or infectious process (eg, appendicitis, diverticulitis) or obstruction of a large tubular structure (eg, intestine). Colicky pain may be more associated with gallstones or kidney stones.

The timing of pain can help to determine the urgency of further testing, although standardized definitions of acute and chronic abdominal pain do not exist.

•First episode of pain lasting less than one week – We consider this to be acute pain that generally requires an extensive ED evaluation unless the history and examination determine a clear cause. (See 'Cause identified by history and physical' below.)

•Recurrent presentations of acute pain – This may be classified as acute, subacute, or chronic pain, and the ED evaluation often depends on the testing and imaging obtained during prior episodes and whether the pain has resolved. Causes may be benign (eg, irritable bowel syndrome, nonincarcerated hernia, nephrolithiasis, abdominal migraines, cyclical vomiting syndrome, cannabis hyperemesis syndrome) or more serious (eg, intermittent ovarian torsion, mesenteric ischemia, biliary disease). High-quality evidence does not exist to define a low-risk patient subset with recurrent abdominal pain that clearly does not need computed tomography (CT) imaging [14].

•Pain that has remained unchanged for months or years – We consider this to be chronic pain that may not require extensive ED evaluation if the patient has had prior testing and imaging. However, a patient with chronic abdominal or flank pain can still present with an acute exacerbation of a chronic problem or a new and unrelated problem, which the history must differentiate. The diagnostic approach to chronic abdominal pain is discussed separately. (See "Evaluation of the adult with abdominal pain", section on 'Diagnostic approach to chronic abdominal pain'.)

●Location of pain — The location and radiation of pain helps narrow the differential diagnosis. The provided tables summarize the causes of pain by characteristic location in the abdomen (table 3) and pelvis (table 4), and the figure demonstrates patterns of referred pain (figure 1). Causes of abdominal pain by location are discussed in detail separately. (See "Causes of abdominal pain in adults".)

Localization by itself, however, is not sufficiently sensitive to definitively exclude intra-abdominal pathology [11,15,16]. As an example, in one study, 24 percent of patients diagnosed with appendicitis had no right lower quadrant pain or tenderness [16]. Right upper quadrant pain is often associated with the liver or gallbladder, although pain from biliary colic can be poorly localized, and patients may complain of lower chest, epigastric, or back discomfort [17].

Pain location can change over time, reflecting progression of disease. As a classic example, appendicitis begins as periumbilical visceral pain (reflecting its embryologic origin) then progresses to right lower quadrant parietal pain as the inflamed appendix (if anterior or pelvic) irritates the peritoneum. Retrocecal appendicitis may not cause any focal peritoneal irritation.

Thoracic diseases, such as pneumonia, pulmonary embolism (PE), or myocardial infarction, can cause upper abdominal pain, particularly in older patients [18]. Many extra-abdominal causes of acute abdominal pain (table 5), such as diabetic ketoacidosis and hypercalcemia, often present with nonlocalizing pain.

●Aggravating and alleviating factors — Examples that help with the differential diagnosis include the following:

•The pain of peptic ulcer disease may change after meals, such as improving with duodenal ulcers or worsening with gastric ulcers. Eating may also exacerbate biliary colic and mesenteric ischemia.

•Pancreatitis pain may improve when the patient sits upright and worsen when the patient reclines.

•A patient with peritonitis often lies still and may note that coughing worsens their pain. Pain that worsens going over bumps during the drive to the ED suggests peritonitis and is roughly 80 percent sensitive, but only 52 percent specific, for appendicitis [19].

•A patient with nephrolithiasis is often restless and cannot find a comfortable position, but this can also occur with vascular catastrophes such as AAA.

•Pain and vomiting that improves with hot showers is characteristic for cannabis hyperemesis syndrome.

•Pain associated with increased physical activity may be cardiac or possibly related to a rectus muscle strain/hematoma.

●Associated symptoms — These include fever, chills, fatigue, weight loss, anorexia, nausea, vomiting, diarrhea, obstipation, constipation, dysuria, diaphoresis, urinary urgency/frequency, hematuria, vaginal discharge/bleeding, penile discharge, and scrotal pain. Examples of diseases that cause abdominal pain with these symptoms are presented in the table (table 6).

Cough, dyspnea, or chest pain suggests an extra-abdominal process such as pneumonia, PE, or myocardial infarction. Extra-abdominal causes may also have abdominal-type associated symptoms, such as nausea or vomiting. Selected extra-abdominal causes of acute abdominal pain are listed in the table (table 5).

●Past medical and social histories and medications – Examples of medical comorbidities, prior surgeries, medications, and misused drugs that increase the risk of diseases that cause abdominal or flank pain are presented in the table (table 7).

Medications associated with constipation are provided in the table (table 8). In an ED patient, however, constipation should be a diagnosis of exclusion after appropriate imaging has been performed or the pain has resolved after a bowel movement.

Victims of intimate partner violence may present to the ED with abdominal or pelvic pain [20,21]. (See "Intimate partner violence: Diagnosis and screening".)

●Past surgical history – A history of previous abdominal surgery increases the risk for small bowel obstruction (SBO), which is from adhesions in 50 to 70 percent of cases. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults".)

Various complications can develop from bariatric surgery, gender-affirming surgery, or receiving an organ transplant, even many years after the procedure. (See 'Organ transplant recipient' below and 'Bariatric surgery' below and "Gender-affirming surgery: Feminizing procedures" and "Gender-affirming surgery: Masculinizing procedures".)

A variety of postoperative complications can cause abdominal pain, such as ileus, surgical site infections, hematoma/seroma formation, and nerve injury. (See "Postoperative ileus" and "Overview of the evaluation and management of surgical site infection" and "Complications of abdominal surgical incisions".)

●Trauma – It is helpful to ask whether the patient sustained any injuries, procedures, or instrumentation in the prior month. Intra-abdominal injuries may not manifest for days to weeks after the event. Splenic rupture is an example, but delayed presentations of perforated bowel, bowel hematomas, pancreatitis, intrabdominal abscess, and injuries to the liver, gallbladder, and genitourinary tract have all been reported. Clinical manifestations of diaphragmatic injury, which is often not diagnosed immediately following the injury, can be delayed for months to even years. (See "Blunt abdominal trauma in adults: Initial evaluation and management" and "Initial evaluation and management of blunt thoracic trauma in adults" and "Recognition and management of diaphragmatic injury in adults".)

●Obstetric/gynecologic history – It is critical to determine pregnancy status and gestational age if the patient is pregnant. Pregnancy broadens the differential diagnosis to include complications of pregnancy (such as an ectopic gestation); round ligament pain; preeclampsia; hemolysis, elevated liver enzymes, low platelet count (HELLP) syndrome; and issues related to spontaneous pregnancy loss. Symptoms in later pregnancy may be atypical as the gravid uterus displaces the traditional location of other intraabdominal organs. (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients".)

We maintain a heightened suspicion for unsafe abortion in a reproductive-age pregnant patient with clinical findings related to the genital tract, as many patients will not report the procedure or the pregnancy. (See "Unsafe abortion", section on 'History'.)

In a nonpregnant female, it is important to ask about menstrual history (eg, last menstrual period, last normal menstrual period, cycle length), dyspareunia, and dysmenorrhea. Recurrent, acute pain related to menstrual cycles suggests a reproductive organ-related etiology. (See "Acute pelvic pain in nonpregnant adult females: Evaluation" and "Chronic pelvic pain in adult females: Evaluation".)

Monthly recurrent pain in a female patient may be associated with the patient's menstrual cycle. Endometriosis pain can be anywhere in the abdomen and is usually recurrent each month. (See "Endometriosis in adults: Clinical features, evaluation, and diagnosis".)

Females undergoing ovulation induction can develop ovarian hyperstimulation syndrome from multiple, large ovarian cysts precipitating acute fluid shifts with depletion of intravascular fluid. (See "Pathogenesis, clinical manifestations, and diagnosis of ovarian hyperstimulation syndrome".)

●Family history – Examples of family history that may be relevant to the differential diagnosis include the following:

•Inflammatory bowel disease in a patient with abdominal pain and bloody diarrhea (see "Definitions, epidemiology, and risk factors for inflammatory bowel disease")

•Familial Mediterranean fever in a patient with recurring attacks of fever and serosal inflammation of the peritoneum, pleura, or synovium (see "Clinical manifestations and diagnosis of familial Mediterranean fever")

•Hereditary angioedema in a patient with recurrent abdominal pain and pseudo-obstruction (see "Hereditary angioedema (due to C1 inhibitor deficiency): Epidemiology, clinical manifestations, exacerbating factors, and prognosis")

●Sick contacts and travel history – Recent travel or similar symptoms among family or friends are important clues indicative of an infectious, environmental, or food-borne etiology. Patients are often in contact with a person with gastroenteritis before developing symptoms themselves. (See "Acute viral gastroenteritis in adults" and "Causes of acute infectious diarrhea and other foodborne illnesses in resource-abundant settings".)

●Occupational history – We do not routinely obtain an occupational history in ED patients, but this may help to identify unusual causes of pain. For example, lead poisoning in an adult (eg, construction worker) can present with abdominal pain, constipation, and anorexia. (See "Overview of environmental health" and "Lead exposure, toxicity, and poisoning in adults: Clinical manifestations and diagnosis", section on 'Clinical manifestations'.)

●Mental health and psychiatric history – Abdominal pain may be related to increased stress or emotional disturbances. Eating disorders, Munchausen syndrome, somatic symptom disorder, and functional neurological symptom disorder (conversion disorder) may also cause abdominal pain. However, these should not interfere with a thorough evaluation of abdominal pain. (See "Eating disorders: Overview of epidemiology, clinical features, and diagnosis" and "Factitious disorder imposed on self (Munchausen syndrome)" and "Somatic symptom disorder: Epidemiology, clinical features, and course of illness" and "Functional neurological symptom disorder (conversion disorder) in adults: Clinical features, assessment, and comorbidity".)

Physical examination

●General appearance and vital signs

•Temperature – Fever increases the suspicion for infection or inflammatory process. Pain often causes tachypnea, which can cause a falsely lower oral temperature measurement [22]. We check a rectal temperature if there is concern about an inaccurate reading. Certain patient populations, such as older adults and those with immunocompromise, may be unable or less likely to develop a fever. (See "Pathophysiology and treatment of fever in adults".)

•Blood pressure and heart rate – Hypotension is an ominous finding in a patient with abdominal or flank pain and may reflect a shock state (eg, hemorrhagic, hypovolemic, septic, endocrine) (table 9). Tachycardia is an early compensatory mechanism in a patient with shock (although may be blunted by certain medications such as beta blockers). The presence of either should prompt resuscitation simultaneously with the evaluation. (See 'Patient with suspected life-threatening abdominal catastrophe' below and "Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock".)

Some patients with acute peritoneal irritation (eg, ruptured ovarian cyst, ectopic pregnancy) and hypotension may not be tachycardic, or may even be bradycardic, likely from a parasympathetic nervous system (ie, vagal) reflex [23]. (See "Evaluation and management of ruptured ovarian cyst", section on 'Clinical findings'.)

•Respiratory rate – An elevated respiratory rate may be due to pain or from a compensatory reaction to an underlying metabolic acidosis.

•General appearance – The patient's general appearance not only provides clues to the diagnosis but also guides the urgency of resuscitation, analgesia, and imaging. The patient who is restless, curled up, and agitated may have renal colic. A patient lying perfectly still in bed with knees bent or experiencing worsening pain when the examiner lightly bumps the stretcher raises concern for peritonitis. Signs of shock (eg, pallor, diaphoresis, altered mental status) warrant resuscitation simultaneously with the evaluation. Signs of systemic disease (eg, spider angiomata in cirrhosis, cachexia in malignancy) are often readily apparent.

●Abdominal examination

•Inspection – General inspection may reveal signs of previous surgeries (eg, incision scar), abdominal pulsations, or distension. Periumbilical ecchymosis (Cullen sign) can occur with pancreatitis, rectus sheath hematoma, perforated ulcer, and intra-peritoneal hemorrhage. Abdominal wall pathology such as a hernia can be obvious if incarcerated but may require asking the patient to increase abdominal pressure (ie, Valsalva maneuver, cough) to elicit the bulge. Examining the patient while they are standing may also help identify hernias. (See "Overview of abdominal wall hernias in adults", section on 'Clinical features'.)

•Palpation – Abdominal palpation identifies the location and degree of tenderness and detects signs of peritoneal irritation, such as involuntary guarding and muscular rigidity. Serial examinations can improve diagnostic accuracy [24].

Our approach is to lightly palpate an area away from the site of pain, then extend towards the area of maximal pain. Once the area of maximal tenderness is localized, we perform maneuvers to elicit peritoneal signs, such as percussion or releasing after deep palpation. If light palpation does not identify a specific area of tenderness, palpate deeper to identify findings such as hepatomegaly, splenomegaly, aortic dilatation, or deep tenderness (such as may occur with retrocecal appendicitis). Percussion may help identify ascites, obstruction, and enlarged organs. In patients with obesity, due to the increased intra-abdominal and subcutaneous adipose tissue, organs may be more difficult to palpate.

A rigid abdomen is cause for concern, but traditional techniques for assessing rebound tenderness have limited sensitivity and specificity for identifying peritonitis [25,26]. Gentler methods to elicit signs of peritoneal irritation include having the patient cough, stand on their toes and drop their heels to the ground, or gently shaking the pelvis or the stretcher [27,28]. The heel test can also be performed by striking a recumbent patient's heel. However, studies of these tests are limited, and their test characteristics remain uncertain [29,30].

Voluntary guarding can occur from nervousness or pain and can be abated via reassurance, warming the clinician's hands prior to palpating, or asking the patient to flex their hips or take a deep breath during the examination.

Patients who are extremely ticklish can be supported by interweaving the clinician's fingers with the patient's fingers to conduct the examination.

Palpating the aorta is safe but generally has limited utility with the availability of point-of-care ultrasound. An abnormal width of aortic pulsation suggests an AAA. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Abdominal palpation' and 'Role of point-of-care ultrasound' below.)

Other examination maneuvers that can be selectively performed include the following:

-Although insensitive, the psoas (right lower quadrant pain with passive right hip extension), obturator (right lower quadrant pain with passive right knee flexion and right hip flexion/internal rotation), and Rovsing signs (right lower quadrant with palpation of the left lower quadrant) have good specificity for appendicitis. (See "Acute appendicitis in adults: Clinical manifestations and differential diagnosis", section on 'Physical examination'.)

-Murphy sign (worsening pain and tenderness during deep inspiration with right upper quadrant palpation) is sensitive but not specific for acute cholecystitis. (See "Acute calculous cholecystitis: Clinical features and diagnosis", section on 'Physical examination'.)

-The presence of Carnett sign (increased abdominal tenderness when the abdominal wall muscles are contracted) suggests pathology within the abdominal wall instead of intraperitoneal. In one small study, Carnett sign was found to be 95 percent accurate at differentiating abdominal wall pain from visceral pain [31].

•Abdominal auscultation – In the ED, this is generally of limited utility since bowel sound findings do not alter the decision to image a patient with abdominal distension. We will occasionally auscultate with light to deep pressure as a means to elicit tenderness with the patient distracted. Periodic rushes of high-pitched "tinkling" bowel sounds or the complete absence of bowel sounds, in the presence of abdominal distention, are signs of bowel obstruction [32]. An abdominal bruit, though rarely appreciated, is indicative of partially obstructed and turbulent blood flow which may be found in renal and splenic artery stenosis, abdominal aortic disease, or other intrabdominal vascular disease.

●Extra-abdominal examination — Examining the following organ systems can provide clues to intra-abdominal and extra-abdominal causes of pain:

•Genital – In a male with lower abdominal or flank pain, examine the scrotum for testicular edema and tenderness, epididymal tenderness, scrotal masses, and cremasteric reflexes. Some patients, particularly young adults, may not initially reveal scrotal symptoms. (See "Acute scrotal pain in adults: Evaluation and management of major causes".)

Perform a pelvic examination in a female with pain and tenderness in the lower half of the abdomen (with shared decision-making with the patient if they believe this examination is unnecessary). There are no pre-examination criteria to determine if the pelvic examination can be deferred or will provide useful information [4]. (See "The gynecologic history and pelvic examination", section on 'Pelvic examination'.)

•Rectal – We selectively perform a rectal examination, since this has questionable utility in a patient with undifferentiated abdominal or flank pain without gastrointestinal bleeding [33,34]. The rectal examination is useful when there is a concern for gastrointestinal bleeding, when there is obstipation (to exclude fecal impaction or foreign body), or when identifying rectal tenderness may change management (eg, a patient may have rectal tenderness and not abdominal tenderness with retrocecal appendicitis).

•Heart and lungs – Auscultate the heart and lungs and palpate a pulse. Atrial fibrillation or valvular disease can increase suspicion for mesenteric ischemia secondary to vascular embolization. Localized decreased or coarse breath sounds raise suspicion for pneumonia.

•Musculoskeletal, back, and flank – Percuss the costovertebral angles as tenderness suggests pyelonephritis. Passively range the hips since intra-articular, retroperitoneal, or psoas-related infectious and inflammatory processes can refer pain to the lower abdomen or flank. Flank ecchymosis (Grey-Turner sign (image 1)) can occur with retroperitoneal hemorrhage, such as from a ruptured AAA or hemorrhagic pancreatitis.

•Eyes – Examine the sclera for icterus.

•Skin – Examine for rashes, especially over the abdomen, back, and perineum. Engorged blood vessels, telangiectasias, petechiae, or jaundice may indicate liver disease. Zoster presents with a rash in the dermatomal distribution of the pain, but the pain often precedes the rash by several days, complicating the diagnosis. (See "Epidemiology, clinical manifestations, and diagnosis of herpes zoster", section on 'Clinical manifestations'.)

Role of point-of-care ultrasound — Emergency physician-performed point-of-care ultrasound has become an important diagnostic tool for patients presenting with abdominal pain. Since ultrasound is rapid and can be performed at the bedside, it is especially helpful in the unstable patient or when there is concern for abdominal catastrophe. However, test characteristics vary depending on the operator, the patient body habitus, and indication [35]. Point-of-care ultrasound can guide further evaluation, initial treatment, and consultations in the following situations:

●When there is concern for hemoperitoneum, such as from ruptured ectopic pregnancy or hemorrhagic ovarian cyst (image 2). (See "Emergency ultrasound in adults with abdominal and thoracic trauma", section on 'Abdominal examination'.)

●To identify an AAA (image 3), although ultrasound cannot exclude a leak or rupture since it has limited utility for detecting retroperitoneal bleeding. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Diagnosis'.)

●In a pregnant patient to identify an intrauterine pregnancy (image 4) and potentially an adnexal or tubal ectopic pregnancy (image 5). (See "Ultrasonography of pregnancy of unknown location".)

●In a hypotensive patient; in addition to hemoperitoneum, ultrasound can identify cardiac and thoracic etiologies and assess the inferior vena cava diameter as an indicator of fluids status. (See "Evaluation of and initial approach to the adult patient with undifferentiated hypotension and shock", section on 'Point-of-care ultrasonography' and "Novel tools for hemodynamic monitoring in critically ill patients with shock", section on 'Vena cava assessment'.)

●In a patient with right upper quadrant pain, to identify gallstones or radiographic signs of cholecystitis (image 6 and image 7). However, emergency physician-performed point-of-care ultrasound may be more helpful in establishing the diagnosis of acute cholecystitis and expediting care rather than excluding the diagnosis. A meta-analysis (7 studies, 1,772 patients) found the sensitivity and specificity of point-of-care ultrasound for cholecystitis was 71 (95% CI 62-78) and 94 (95% CI 88-98) percent, respectively [36]. (See "Clinical manifestations and evaluation of gallstone disease in adults", section on 'Transabdominal ultrasound' and "Acute calculous cholecystitis: Clinical features and diagnosis", section on 'Ultrasonography'.)

●In a patient with urinary retention, to confirm a distended bladder. (See "Acute urinary retention", section on 'Initial evaluation'.)

●In a patient with flank pain, the presence of unilateral hydronephrosis suggests an obstructive kidney stone (image 8). (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Ultrasound of the kidneys and bladder'.)

Depending on operator experience with the following indications, point-of-care ultrasound can be performed for initial screening but ultimately may need radiology confirmation:

●In a nonpregnant female, to identify ovarian and uterine pathology and ovarian blood flow (on color Doppler). (See "Ovarian and fallopian tube torsion", section on 'Ultrasound' and "Adnexal mass: Ultrasound categorization".)

●In a male with acute scrotal pain, the absence of Doppler flow suggests testicular torsion. (See "Acute scrotal pain in adults: Evaluation and management of major causes".)

●In a patient with right lower quadrant pain, ultrasound can identify appendicitis, but it is often technically challenging to find the appendix. (See "Acute appendicitis in adults: Diagnostic evaluation", section on 'Ultrasound'.)

●In a patient with suspected SBO, ultrasound can identify dilated loops of bowel. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Bedside imaging study'.)

●In patients with suspected pancreatitis, ultrasound may detect a pancreatic pseudocyst. (See "Approach to walled-off pancreatic fluid collections in adults", section on 'Radiologic imaging'.)

●Abdominal free air can be identified on ultrasound, but it is not the accepted study of choice for this indication. (See "Indications for bedside ultrasonography in the critically ill adult patient", section on 'Detection of abdominal free air'.)

●Lower lobe pneumonia or a hemo/pneumothorax may be identified by lung ultrasound. (See "Clinical evaluation and diagnostic testing for community-acquired pneumonia in adults", section on 'Ultrasound and other studies' and "Bedside pleural ultrasonography: Equipment, technique, and the identification of pleural effusion and pneumothorax", section on 'Evaluation for pneumothorax'.)

Ancillary studies — These are useful adjuncts but should not be used to definitively exclude a diagnosis.

●Laboratory tests — We obtain laboratory studies in most patients unless the history and physical examination establish the cause of the pain (eg, incarcerated hernia with improvement of pain after reduction, zoster rash in same distribution as pain). The threshold for ordering a broader range of tests is lower in the patient with immunosuppression, older age, and significant underlying disease (eg, diabetes, cancer, human immunodeficiency virus [HIV], cirrhosis). Laboratory tests to evaluate acute abdominal and flank pain include the following:

•Pregnancy test – Either a urine or serum qualitative human chorionic gonadotropin (hCG) test is required in all females of childbearing age with abdominal pain. Both tests are extremely sensitive. Patient self-assessment of pregnancy status is not reliable [37]. Obtain a quantitative serum hCG in a pregnant patient without a previously documented intrauterine pregnancy. (See "Ectopic pregnancy: Clinical manifestations and diagnosis", section on 'Human chorionic gonadotropin'.)

•Complete blood count (CBC) – Although frequently ordered, the CBC is nonspecific and rarely alters management [38-40]. A leukocytosis or neutrophil left shift can support the presence of an acute infectious or inflammatory process. While up to 80 percent of patients with acute appendicitis have a leukocytosis, 70 percent of patients with other causes of right lower quadrant abdominal pain also have a leukocytosis [40,41]. Healthy pregnant patients typically have a mild leukocytosis. (See "Maternal adaptations to pregnancy: Hematologic changes", section on 'White blood cells'.)

•Basic electrolytes – Electrolytes are frequently measured but rarely alter management. They can identify metabolic acidosis (eg, diabetic ketoacidosis [DKA]) and electrolyte or free water losses. In patients with diabetes, disruption of typical glucose levels or glucose control patterns may result from acute intrabdominal pathology (as opposed to being a symptom of DKA) [42]. Electrolytes can assess for impaired kidney function, which is a risk factor for contrast-induced acute kidney injury. (See "Prevention of contrast-induced acute kidney injury associated with computed tomography", section on 'Risk factors'.)

•Serum lactate, venous blood gas – Although nonspecific, an elevated serum lactate can indicate sepsis or bowel ischemia and can be used to follow the response to resuscitation. A venous blood gas can accurately measure blood pH from a metabolic acidosis accompanying intrabdominal pathology and provide an additional marker for resuscitation response. (See "Overview of intestinal ischemia in adults", section on 'Laboratory studies' and "Sepsis syndromes in adults: Epidemiology, definitions, clinical presentation, diagnosis, and prognosis", section on 'Laboratory signs'.)

•Liver and pancreatic enzymes – Measure these in a patient with upper abdominal pain. As compared with amylase, serum lipase is more sensitive and specific for pancreatitis, but elevations may be caused by other diseases. Marked liver enzyme elevation suggests acute hepatitis (eg, viral) but can occur with underlying chronic liver disease (eg, Wilson disease), ischemic or drug-induced liver injury (eg, acetaminophen), rhabdomyolysis, malignancy, or an autoimmune disorder. Elevation in the serum total bilirubin and alkaline phosphatase concentrations suggest a cholestatic pattern and are uncommon in uncomplicated cholecystitis. (See "Approach to the patient with abnormal liver tests" and "Clinical manifestations, diagnosis, and natural history of acute pancreatitis" and "Approach to the patient with elevated serum amylase or lipase".)

•Coagulation studies and blood type – Obtain these in a patient with gastrointestinal bleeding or with a high index of suspicion that an operation will be necessary. A pregnant patient with vaginal bleeding should have a blood type and Rh checked.

•Erythrocyte sedimentation rate, C-reactive protein – Although nonspecific these acute phase reactants may be elevated in inflammatory and infectious processes. (See "Acute phase reactants".)

•D-dimer – Can be elevated in vascular occlusive diseases, such as acute aortic syndromes [43,44]. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Laboratory studies and biomarkers' and "Clinical features and diagnosis of acute aortic dissection", section on 'D-dimer'.)

•Urinalysis – The presence of pyuria or hematuria suggests a urinary tract infection (UTI) but can also occur with any inflammatory process adjacent to a ureter. For example, 20 to 48 percent of patients with appendicitis have blood, leukocytes, or bacteria in their urine [45,46]. Many older adults have chronic, mild pyuria. Hematuria may be present in as many as 87 percent of patients with AAA, which can lead to a misdiagnosis of nephrolithiasis [47]. (See "Acute simple cystitis in female adults" and "Acute simple cystitis in male adults".)

•Sexually transmitted infection (STI) testing – During the pelvic examination in a female with lower abdominal pain, swabs can be obtained for nucleic acid amplification testing for gonorrhea, chlamydia, and trichomonas. (See "Clinical manifestations and diagnosis of Neisseria gonorrhoeae infection in adults and adolescents", section on 'Nucleic acid amplification' and "Clinical manifestations and diagnosis of Chlamydia trachomatis infections in adults and adolescents", section on 'Nucleic acid amplification testing (test of choice)'.)

●Chest radiograph (CXR) — Obtain a CXR in a patient with abdominal pain who also has associated cardiothoracic symptoms (eg, cough, dyspnea, chest pain) to assess for pneumonia, pneumothorax, or other pleural-based processes. Pleural irritation from a basilar lung infiltrate can cause sharp abdominal pain that is aggravated by cough or deep inspiration. An upright CXR can also visualize pneumoperitoneum occurring from hollow viscous perforation. (See "Clinical evaluation and diagnostic testing for community-acquired pneumonia in adults" and 'Imaging' below.)

●Electrocardiogram (ECG) – Obtain an ECG in a patient with upper abdominal pain who has older age, immunosuppression, or significant underlying disease (eg, diabetes, cancer, HIV, cirrhosis). Some patients with an acute coronary syndrome, especially older adults and those with diabetes, present with epigastric pain, nausea, or vomiting rather than chest pain. Abdominal pain is the presenting complaint for an acute myocardial infarction in approximately one-third of these atypical cases. Newly diagnosed atrial fibrillation raises concern for acute mesenteric arterial occlusion caused by embolism from dislodged thrombus from the left atrium. (See "Initial evaluation and management of suspected acute coronary syndrome (myocardial infarction, unstable angina) in the emergency department", section on 'Atypical presentations' and "Acute mesenteric arterial occlusion", section on 'Arterial embolism'.)

●Abdominal paracentesis – In a patient with ascites and abdominal pain or tenderness, a diagnostic paracentesis should be performed and ascitic fluid analyzed to exclude spontaneous bacterial peritonitis. (See "Diagnostic and therapeutic abdominal paracentesis" and "Spontaneous bacterial peritonitis in adults: Diagnosis", section on 'Obtaining ascitic fluid'.)

Overview of common imaging modalities — The decision to image an ED patient with abdominal or flank pain is a clinical judgment based on whether there are entities on the differential diagnosis that must be excluded during the current visit or can wait for outpatient follow-up. This is often a complex decision-making process and may require shared decision-making with the patient in equivocal cases. Decisions regarding the need and timing of imaging are based on suspected etiologies and are discussed in more detail below. (See 'Patient with suspected life-threatening abdominal catastrophe' below and 'Patient without abdominal catastrophe' below.)

Most patients with abdominal tenderness or distension, pain requiring multiple opioid doses, high-risk features (table 1), or leukocytosis will require imaging. It can be helpful to have a discussion with the radiologist if unsure which study to order or whether contrast administration is necessary. Common ED imaging modalities include the following:

●CT scan — This is the modality of choice in the ED evaluation of undifferentiated abdominal pain [48]. Approximately two-thirds of patients presenting to the ED with acute abdominal pain have a disease that can be diagnosed by CT [49]. One small study found that CT correctly diagnosed the cause of pain among patients with an "acute abdomen" in 90 percent of cases compared with 76 percent of cases diagnosed correctly by history and physical examination alone [50]. CT is particularly useful in older adults, establishing or suggesting the diagnosis in 75 percent of cases and 85 percent of emergency surgical conditions [9]. Unenhanced CT is extremely sensitive in identifying free air [48].

•Role of intravenous (IV) contrast — Routine administration of IV contrast improves the diagnostic accuracy of CT for many diagnoses [51]. However, acute kidney injury may develop after administration of iodinated contrast material, primarily in patients with an estimated glomerular filtration rate (eGFR) <30 mL/min/1.73 m². If unsure, the radiologist can help determine if IV contrast is necessary. (See "Patient evaluation prior to oral or iodinated intravenous contrast for computed tomography" and "Prevention of contrast-induced acute kidney injury associated with computed tomography".)

•Role of oral contrast — Improvements in the image quality provided by multislice helical CT scanners have raised questions about the need for oral contrast. Most institutions do not routinely use oral contrast because of associated delays in study acquisition, need for nasogastric tube insertion in a patient unable to tolerate orally administered contrast, and prolonged ED stay with questionable diagnostic benefit [52,53]. The CT can be repeated with oral contrast in the rare case of an equivocal IV contrast-enhanced CT. However, oral contrast may increase diagnostic yield in patients with little body fat, those with extensive bowel anatomy changing surgery, and those with suspected inflammatory bowel disease.

One prospective study compared the performance of noncontrast and oral contrast-enhanced CT in a convenience sample of patients with acute abdominal pain and found the two modalities had a simple agreement of 79 percent (95% CI 70-87) [54]. Another prospective study of a convenience sample of 72 ED patients presenting with acute nontraumatic abdominal pain who were initially evaluated with a noncontrast CT found no missed consequential diagnoses (defined as causing death or requiring abdominal surgery) in the seven days following ED evaluation [55].

●Radiology-performed ultrasound – Ultrasound is the study of choice to evaluate the biliary tract, pregnancy, and reproductive organs but can also be used to identify appendicitis and obstructive uropathy (such as from nephrolithiasis).

●Magnetic resonance imaging (MRI) – MRI is an accurate alternative to CT for excluding intra-abdominal pathology (eg, appendicitis) when trying to avoid radiation exposure (eg, pregnancy). (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients", section on 'Imaging'.)

Magnetic resonance angiography (MRA) is an option in patients with an allergy to iodinated contrast and a heightened concern for mesenteric ischemia. (See "Overview of intestinal ischemia in adults", section on 'Advanced abdominal imaging'.)

●Plain abdominal radiographs — We do not routinely obtain plain abdominal radiographs for abdominal or flank pain as this practice is extremely low yield [56,57]. Plain radiographs can expedite the evaluation when bowel obstruction, bowel perforation, or a radiopaque foreign body is suspected but cannot be relied upon to exclude these disorders [58]. In an ED patient without these indications and for whom a CT is planned, plain abdominal radiographs are unhelpful, may delay definitive diagnosis, and can sometimes be misleading [59,60].

PATIENT WITH SUSPECTED LIFE-THREATENING ABDOMINAL CATASTROPHE

Differential diagnosis of abdominal catastrophe — The following are abdominal processes that can cause ischemia, sepsis, or hemorrhage and become a life-threatening abdominal catastrophe (manifestations and risk factors are summarized in the table (table 10)):

●Abdominal aortic aneurysm (AAA) – Can present with abdominal, back, or flank pain and/or hematuria while rupture typically produces acute, severe pain and hypotension. Pain can be migratory and associated with distal neurologic symptoms. (See "Clinical features and diagnosis of abdominal aortic aneurysm" and "Epidemiology, risk factors, pathogenesis, and natural history of abdominal aortic aneurysm", section on 'Risk factors for the development of AAA'.)

●Descending aortic dissection – Abdominal pain can develop if the dissection extends or causes splenic, kidney, or bowel infarction. (See "Clinical features and diagnosis of acute aortic dissection".)

●Mesenteric ischemia – This can be differentiated into four entities (see "Overview of intestinal ischemia in adults"):

•Mesenteric arterial occlusion (embolic or thrombotic) - classically described as having minimal findings on abdominal examination ("pain out of proportion to the exam") (see "Acute mesenteric arterial occlusion")

•Nonocclusive mesenteric ischemia (low flow state or vasoconstriction) (see "Nonocclusive mesenteric ischemia")

•Venous thrombosis (see "Mesenteric venous thrombosis in adults")

•Chronic mesenteric ischemia (intestinal angina) (see "Chronic mesenteric ischemia")

●Hollow viscous perforation and/or peritonitis – The most common cause of stomach and duodenal perforation is peptic ulcer disease, but perforation can also complicate appendicitis, diverticulitis, bowel obstruction, ischemic bowel, toxic megacolon, severe retching (ie, esophageal perforation, Boerhaave syndrome), and other processes. Mortality increases in older adults (who are often unaware they have peptic ulcer disease until a complication develops) and with delays in diagnosis. (See "Overview of gastrointestinal tract perforation" and "Overview of complications of peptic ulcer disease" and "Management of acute appendicitis in adults", section on 'Unstable patients or patients with free perforation' and "Acute colonic diverticulitis: Surgical management", section on 'Perforation with generalized peritonitis' and "Boerhaave syndrome: Effort rupture of the esophagus".)

●Bowel strangulation and/or intestinal gangrene – When this complicates processes such as bowel obstruction, volvulus, or incarcerated hernia, mortality rates increase with increasing delays in surgery. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults" and "Large bowel obstruction" and "Gastric volvulus in adults" and "Cecal volvulus" and "Sigmoid volvulus" and "Overview of abdominal wall hernias in adults" and "Clinical manifestations, diagnosis, and prognosis of Crohn disease in adults", section on 'Clinical features'.)

●Intra-abdominal abscess – Diverticulitis is the most common cause, and other common sites include liver, kidney, genital tract, and psoas muscle. (See "Pyogenic liver abscess" and "Invasive liver abscess syndrome caused by Klebsiella pneumoniae" and "Renal and perinephric abscess" and "Tubo-ovarian abscess: Management and complications" and "Posthysterectomy pelvic abscess" and "Psoas abscess" and "Clinical manifestations and diagnosis of acute colonic diverticulitis in adults", section on 'Abscess'.)

●Biliary sepsis – Can be from cholangitis or acute cholecystitis. (See "Acute cholangitis: Clinical manifestations, diagnosis, and management" and "Acute calculous cholecystitis: Clinical features and diagnosis".)

●Splenic rupture – Some causes include infectious mononucleosis, trauma, and endoscopic manipulation. (See "Management of splenic injury in the adult trauma patient" and "Infectious mononucleosis", section on 'Management of complications'.)

●Necrotizing pancreatitis – This complication of acute pancreatitis increases risk for organ failure and shock and has a higher mortality. (See "Clinical manifestations, diagnosis, and natural history of acute pancreatitis" and "Management of acute pancreatitis", section on 'Management of complications'.)

●Urinary sepsis – Common causes include pyelonephritis, obstructing nephrolithiasis, urinary tract abnormalities, and recent instrumentation. (See "Acute complicated urinary tract infection (including pyelonephritis) in adults", section on 'Complications' and "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Complications'.)

●Ectopic pregnancy – Classic triad amenorrhea, pelvic pain, and vaginal bleeding is often not present. (See "Ectopic pregnancy: Clinical manifestations and diagnosis" and "Ectopic pregnancy: Epidemiology, risk factors, and anatomic sites".)

●Other pregnancy complications – These include acute placental abruption, necrotic retained products of conception leading to sepsis or toxic shock syndrome, complications of pregnancy termination (including unsafe abortion), and uterine rupture. (See "Acute placental abruption: Pathophysiology, clinical features, diagnosis, and consequences" and "Retained products of conception in the first half of pregnancy", section on 'Patients who are hemodynamically unstable' and "Overview of pregnancy termination", section on 'Complications' and "Unsafe abortion", section on 'Management' and "Uterine rupture of the unscarred uterus: Risk factors, clinical manifestations, management, and outcome" and "Uterine rupture after previous cesarean birth: Prediction, clinical manifestations, diagnosis, management, and outcome".)

●Spontaneous bacterial peritonitis (SBP) – SBP should be excluded with a diagnostic abdominal paracentesis in a patient with cirrhosis and fever, hypothermia, abdominal pain, altered mental status, diarrhea, ileus, or hypotension. (See "Spontaneous bacterial peritonitis in adults: Clinical manifestations" and "Spontaneous bacterial peritonitis in adults: Diagnosis".)

●Fournier gangrene – This is a necrotizing fasciitis of the perineum that begins abruptly with severe pain, redness, edema, and induration and spreads rapidly to the anterior abdominal wall and the gluteal muscles. (See "Necrotizing soft tissue infections".)

●Toxic megacolon – This typically presents with at least one week of severe bloody diarrhea followed by acute colonic dilatation. (See "Toxic megacolon".)

●Toxic shock syndrome – Commonly includes abdominal pain, nausea, vomiting, and diarrhea in addition to the characteristic manifestations of fever, rash, hypotension, and multiorgan dysfunction. This has been associated with retained female hygiene products. (See "Staphylococcal toxic shock syndrome".)

●Ruptured hemorrhagic ovarian cyst – Most hemorrhagic cysts stop bleeding spontaneously, and shock is uncommon. (See "Evaluation and management of ruptured ovarian cyst", section on 'Hemodynamic instability'.)

Resuscitation — Rapidly initiate treatment when there is a concern for an abdominal catastrophe. This includes emergency department (ED) patients with peritonitis, hypotension or other signs of shock, or toxic appearance. Algorithms summarizing the approach to abdominal pain in adult males, nonpregnant females (algorithm 1), and pregnant females with hemodynamic instability or peritonitis (algorithm 2) are provided. The resuscitation is performed simultaneously with the initial evaluation and includes the following:

●Address airway, breathing, and circulation ("ABCs") and obtain laboratory studies – Stabilize airway and breathing as needed. Place the patient on a cardiac monitor and provide supplemental oxygen. Establish large-bore venous access to obtain laboratory studies and start intravenous (IV) fluids (ie, crystalloid). Vasopressors may be needed for suspected sepsis when fluids do not improve hemodynamics. Administer stress-dose glucocorticoids (eg, dexamethasone, hydrocortisone) if adrenal insufficiency is suspected (eg, chronic glucocorticoid therapy, history of primary adrenal insufficiency). Perform a bedside fingerstick glucose in any seriously ill patient or a patient with known diabetes to assess for hyperglycemia and possible diabetic ketoacidosis. Obtain an electrocardiogram to screen for cardiac and electrolyte problems. Do not allow oral consumption of food or drink in anticipation of possible surgical intervention. (See 'Ancillary studies' above and "The decision to intubate" and "Evaluation and management of suspected sepsis and septic shock in adults", section on 'Initial therapy' and "Treatment of adrenal insufficiency in adults", section on 'Adrenal crisis'.)

●Perform point-of-care ultrasound – We rapidly perform a bedside ultrasound to examine for an AAA, free intraperitoneal fluid (concerning for hemoperitoneum), pericardial effusion, or hydronephrosis and to measure the inferior vena cava diameter as an indicator of fluids status. (See 'Role of point-of-care ultrasound' above and "Novel tools for hemodynamic monitoring in critically ill patients with shock", section on 'Vena cava assessment'.)

●Transfuse blood products if concern for hemorrhage – Transfuse blood products in a hemodynamically unstable patient suspected to be hemorrhaging (eg, ruptured AAA, gastrointestinal hemorrhage, ectopic pregnancy, ovarian cyst). (See "Massive blood transfusion" and "Use of blood products in the critically ill".)

●Administer empiric antibiotics – Administer empiric broad-spectrum antimicrobial therapy as soon as possible to a critically ill patient with concern for abdominal sepsis or peritonitis. In general, empiric regimens for intra-abdominal infections include antimicrobial activity against enteric streptococci, coliforms, and anaerobes. Tables summarizing empiric antibiotic regimens for high-risk (table 11) and health care-associated intra-abdominal infections (table 12) are provided. A table and algorithm for empiric broad-spectrum antimicrobial regimens for urinary sources are also provided (table 13 and algorithm 3). (See "Antimicrobial approach to intra-abdominal infections in adults", section on 'Empiric antimicrobial therapy' and "Acute complicated urinary tract infection (including pyelonephritis) in adults", section on 'Empiric antimicrobial therapy'.)

Specialty consultation — We consult procedural specialists early in the patient's ED course since surgical intervention and/or percutaneous drainage are often necessary to obtain source control of intra-abdominal infections (other than spontaneous bacterial peritonitis [SBP]) or to obtain hemostasis of intra-peritoneal hemorrhage. Do not delay consultation while awaiting definitive imaging when there is high clinical suspicion for an abdominal catastrophe. Depending on the preliminary diagnosis, we consult either a general or vascular surgeon, gynecologist, urologist, gastroenterologist, or interventional radiologist, such as in the following circumstances:

●Percutaneous abscess drainage is preferred for an intrabdominal abscess, but surgical intervention may be required to close an anatomic breach or debride infected necrotic tissue. (See "Antimicrobial approach to intra-abdominal infections in adults", section on 'Source control and drainage'.)

●An obstructing infected kidney stone is a urologic emergency that requires rapid decompression either by a ureteral stent or a percutaneous nephrostomy tube. (See "Kidney stones in adults: Surgical management of kidney and ureteral stones", section on 'Emergency surgery'.)

●A ruptured AAA or ectopic pregnancy will often require definitive surgical hemostasis. (See "Management of symptomatic (non-ruptured) and ruptured abdominal aortic aneurysm", section on 'Ruptured AAA' and "Tubal ectopic pregnancy: Surgical treatment", section on 'Indications'.)

●Septic shock from cholecystitis is typically treated with percutaneous cholecystostomy or surgical cholecystectomy. (See "Treatment of acute calculous cholecystitis", section on 'Gallbladder drainage'.)

●Cholangitis often requires biliary drainage with an endoscopic retrograde cholangiopancreatography (ERCP). (See "Acute cholangitis: Clinical manifestations, diagnosis, and management", section on 'Biliary drainage'.)

●Ovarian or testicular torsion requires urgent intervention from a gynecologist or urologist, respectively. (See "Ovarian and fallopian tube torsion", section on 'Management' and "Acute scrotal pain in adults: Evaluation and management of major causes", section on 'Management'.)

●Some processes may need gastroenterology consultation for urgent upper endoscopy (eg, bleeding gastric/peptic ulcer) or colonoscopy (eg, inflammatory bowel disease, sigmoid volvulus). (See "Overview of upper gastrointestinal endoscopy (esophagogastroduodenoscopy)", section on 'Indications' and "Overview of colonoscopy in adults", section on 'Indications'.)

Imaging — In a patient with concern for an abdominal catastrophe, the choice of imaging (beyond point-of-care ultrasound) depends upon the acuity of the presentation, the patient's capacity to tolerate a study, stability for transport to radiology, risk of not diagnosing the etiology versus risk of transport to radiology, and consultant requirements for operative planning. The timing of imaging may need to be coordinated with the procedural consultant and/or intensivist, since resuscitation may need to be continued until the patient is stable for advanced imaging or a definitive procedure.

●In a patient who stabilizes with initial resuscitation, it is reasonable to follow the imaging approach discussed below. (See 'Patient without abdominal catastrophe' below.)

●In a patient with concern for sepsis of abdominal origin or hollow viscous perforation, obtain a portable upright chest radiograph (CXR), which is the initial screening study for pneumoperitoneum (image 9). Immediate surgical consultation is required if pneumoperitoneum is identified. An upright CXR detects as little as 1 to 2 mL of free air after the patient has been upright for 5 to 10 minutes compared with approximately 5 mL detected by a plain abdominal radiograph [49,61]. An upright lateral CXR is even more sensitive for pneumoperitoneum (image 10 and image 11) [62]. (See "Overview of gastrointestinal tract perforation", section on 'Chest imaging'.)

The location of the perforation determines the likelihood of detecting pneumoperitoneum, which is present in only two-thirds of gastroduodenal perforation and in only one-third of perforation of the distal small bowel or large bowel. Sensitivity decreases further in patients with previous abdominal surgery or a walled-off perforation [61].

A left lateral decubitus radiograph can be obtained in patients too ill for upright films and may detect pneumoperitoneum under the diaphragm above the liver edge (image 12). Detection can be improved by placing a nasogastric tube and injecting 50 mL of air or water-soluble contrast, but this is rarely performed unless the patient is too unstable to be moved for computed tomography (CT) scan.

●In a patient without a diagnosis and management plan after point-of-care ultrasound and/or upright CXR (if performed), we obtain an abdominopelvic CT scan, which is the imaging modality most likely to provide the diagnosis in a patient with an abdominal catastrophe. In a hemodynamically stable patient, the risk of not diagnosing the etiology will often outweigh the risk of transporting the patient to radiology. IV contrast is preferred if concerned for an AAA, aortic dissection, or mesenteric ischemia, but hemorrhage from leaking or ruptured AAA can also be visualized on nonenhanced CT (image 13). (See 'Overview of common imaging modalities' above.)

In a patient suspected of having a ruptured AAA, CT confirms the rupture and evaluates feasibility of endovascular repair. However, in a hemodynamically unstable patient with a known AAA or point-of-care ultrasound-visualized AAA, CT imaging is desirable for the surgeon but is not absolutely required prior to intervention. Imaging decisions in the unstable patient should be made in consultation with the surgeon or proceduralist. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Imaging symptomatic patients'.)

●In a patient with biliary, kidney, pregnancy-related, or ovarian pathology, the surgeon or proceduralist may request a radiology-performed ultrasound for further evaluation. If the patient is hemodynamically unstable and point-of-care ultrasound images confirm a diagnosis, we discuss with the surgeon or proceduralist whether the risks of definitive treatment delay and patient transport to radiology for an additional study are outweighed by any additional information that study may provide.

PATIENT WITHOUT ABDOMINAL CATASTROPHE

Evaluation in pregnant patients — The approach to acute abdominal or pelvic pain in a hemodynamically stable pregnant patient without peritonitis is provided in the algorithm (algorithm 4) and discussed in detail separately. (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients".)

Testing decisions must account for the physiologic changes that occur in pregnancy and the desire to avoid ionizing radiation exposure. As examples, a pregnant patient can have fewer clinical findings and may not demonstrate peritoneal signs, possibly because the peritoneum is desensitized to irritation from the gradual growth and stretching [63,64]. Round ligament pain, nausea, and vomiting can occur early in pregnancy. White blood cell counts increase to a normal range of 10,000 to 14,000 cells/mm³. There is a modest increase in baseline heart rate (10 to 15 beats per minutes). (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients", section on 'Physiologic changes of pregnancy that impact differential diagnosis'.)

The enlarged uterus can make localizing pain challenging, although with appendicitis, the area around the McBurney point is still the most common location of tenderness regardless of gestational age. (See "Acute appendicitis in pregnancy", section on 'Clinical features'.)

●Abdominal and pelvic ultrasound – We start with an ultrasound to evaluate the pregnancy (if documented intrauterine pregnancy), to evaluate for ectopic pregnancy (if undocumented intrauterine pregnancy), and to assess for other causes such as appendicitis, nephrolithiasis, gallbladder disease, and uterine rupture. (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients", section on 'Imaging' and "Ultrasonography of pregnancy of unknown location" and "Ectopic pregnancy: Clinical manifestations and diagnosis", section on 'Transvaginal ultrasound'.)

●Abdominopelvic magnetic resonance imaging (MRI) – If the cause of abdominal pain is not consistent with an obstetric etiology (eg, appendicitis), or other potentially serious abdominal pathology cannot be excluded clinically or by ultrasound, we obtain an abdominopelvic MRI (without gadolinium), which is as accurate as computed tomography (CT) for the diagnosis of many disorders but does not expose the patient to ionizing radiation. CT can be performed when clinical findings and ultrasound examination are equivocal and MRI is not available. (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients", section on 'Imaging'.)

Evaluation in nonpregnant patients — An algorithm summarizing the approach to abdominal pain in adult males and nonpregnant females (algorithm 1) is provided.

Cause identified by history and physical — In a patient in whom the history, examination, and laboratory studies (if performed) identify a clear etiology, further testing can often be deferred or avoided. Examples of such scenarios include the following:

●A patient with umbilical or inguinal pain and bulge that resolves after reduction of the hernia. However, an incarcerated hernia that is not easily reduced can cause severe pain and require immediate surgical consultation. (See "Overview of abdominal wall hernias in adults" and "Classification, clinical features, and diagnosis of inguinal and femoral hernias in adults".)

●A patient with a zoster rash in the dermatomal distribution of the pain. (See "Epidemiology, clinical manifestations, and diagnosis of herpes zoster", section on 'Clinical manifestations'.)

●A patient with crampy diffuse abdominal pain, no abdominal tenderness, and complete resolution of pain after a bowel movement. However, constipation is a diagnosis of exclusion in an emergency department (ED) patient with ongoing pain.

●A patient with non-bloody diarrhea (with or without vomiting and fever) that is more prominent than the abdominal pain, especially if there was recent travel or similar symptoms among close contacts. Although common, gastroenteritis and foodborne diseases are typically diagnoses of exclusion in the ED, but imaging can often be avoided in a patient with improving symptoms and a low suspicion for alternate etiology. (See "Acute viral gastroenteritis in adults" and "Approach to the adult with acute diarrhea in resource-abundant settings" and "Approach to the adult with acute diarrhea in resource-limited settings" and "Causes of acute infectious diarrhea and other foodborne illnesses in resource-abundant settings".)

●A young patient (eg, <40 years old) with intermittent, burning epigastric pain that occurs several hours after meals, associated gastroesophageal reflux, normal laboratory studies, and a nontender abdominal examination. However, we do not definitively diagnose an ED patient with gastritis, reflux, or peptic ulcer disease since upper gastrointestinal endoscopy confirms the diagnosis and is not routinely performed in the ED. Also, intermittent upper abdominal pain can be a symptom of other diseases, such as biliary colic and acute coronary syndrome. In these circumstances, especially when imaging is deferred, it is prudent to diagnose nonspecific abdominal pain, provide clear ED return precautions, and encourage outpatient follow-up for re-evaluation. (See "Peptic ulcer disease: Clinical manifestations and diagnosis".)

●A young male patient with right lower quadrant pain/tenderness or a patient with left lower quadrant pain/tenderness and a prior history of diverticular disease may be diagnosed clinically with appendicitis or diverticulitis, respectively. These scenarios are discussed further below. (See 'Other patients (eg, lower abdominal pain)' below.)

●A young patient with a history of kidney stones confirmed on prior imaging, no suspicion for a serious alternative diagnosis (eg, cholecystitis, appendicitis, abdominal aortic aneurysm (AAA), typical pain syndrome, hematuria, and no fever or signs of shock. (See 'Flank pain or abnormal testicular examination' below.)

Cause not identified by history and physical

Suspected acute vascular process — A patient with severe, sudden-onset abdominal pain that is out of proportion to findings on examination, especially with a history of atherosclerosis or dysrhythmia, should be evaluated for an acute vascular process. (See 'Differential diagnosis of abdominal catastrophe' above.)

●Preferred imaging: CT angiography (CTA) – We obtain an intravenous (IV) contrast-enhanced chest/abdomen/pelvis CTA in a patient with heightened concern for mesenteric ischemia, aortic dissection, or abdominal aortic aneurysm (AAA). A CTA accurately visualizes the mesenteric vasculature, shows changes consistent with bowel infarction, and is less invasive compared with standard angiography [65]. A CTA also reliably identifies other abdominal pathology when ischemia is not the cause of abdominal pain [66]. (See "Overview of intestinal ischemia in adults", section on 'Advanced abdominal imaging' and "Chronic mesenteric ischemia", section on 'Vascular imaging' and "Clinical features and diagnosis of acute aortic dissection", section on 'Cardiovascular imaging'.)

●Alternative imaging options

•Abdominopelvic CT (non-angiography) – Although not as accurate as a CTA, an IV contrast-enhanced or nonenhanced CT can still be diagnostic. CT has a sensitivity of nearly 100 percent in diagnosing AAA, and compared with ultrasound, it is not limited by bowel gas or body habitus. Hemorrhage from leaking or ruptured AAA can be visualized on nonenhanced CT, making IV contrast unnecessary in emergency situations or when IV contrast may be contraindicated. (See "Clinical features and diagnosis of abdominal aortic aneurysm", section on 'Imaging symptomatic patients'.)

An IV contrast-enhanced abdominopelvic CT will screen for ischemia and evaluate for other potential etiologies in a patient with a less specific clinical presentation [52]. (See "Overview of intestinal ischemia in adults", section on 'Advanced abdominal imaging'.)

•Magnetic resonance angiography (MRA) – MRA may be necessary in a patient with an allergy to iodinated contrast and a heightened concern for mesenteric ischemia. MRA is also more sensitive than CT for diagnosing mesenteric venous thrombosis. (See "Overview of intestinal ischemia in adults", section on 'Advanced abdominal imaging' and "Mesenteric venous thrombosis in adults", section on 'Imaging'.)

Plain radiographs in patients with mesenteric ischemia are often unremarkable and therefore should not be obtained in patients with a suspected acute vascular process. The presence of radiographic findings suggests late disease and correlates with increased mortality. Findings include ileus, "thumbprinting" (large bowel wall thickening with edematous haustra at regular intervals), and intramural air (pneumatosis intestinalis). In one study, patients with these findings had a mortality of 78 percent compared with 29 percent in patients with normal radiographs [67].

Suspected intestinal obstruction — Signs and symptoms suggesting bowel obstruction include nausea, vomiting, cramping periumbilical or diffuse abdominal pain, increased belching, obstipation, and abdominal distension. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Clinical presentations' and "Large bowel obstruction", section on 'Clinical presentations'.)

Imaging decisions are guided by the acuity of the presentation and history of prior episodes of obstruction, especially if abdominopelvic CT scans were obtained during prior episodes. We obtain plain abdominal radiographs (including upright chest radiograph [CXR]) in a patient suspected of having a bowel obstruction to quickly confirm the diagnosis, expedite consultation, and exclude findings that indicate the need for immediate intervention (eg, pneumoperitoneum, volvulus, pneumatosis intestinalis). This is typically followed by abdominopelvic CT to further characterize the nature, severity, and potential etiologies of the obstruction. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Preferred initial studies for most patients' and "Large bowel obstruction", section on 'Imaging'.)

●Initial imaging in most patients: Plain abdominal radiographs — These are approximately 80 percent sensitive and 70 to 80 percent specific for diagnosing a small bowel obstruction (SBO) but can be "normal, nonspecific, or misleading" in 10 to 20 percent of patients. An SBO is likely if the small bowel is dilated >2.5 cm, there is gaseous distention, or air-fluid levels are present (image 14 and image 15) [68]. The radiographic finding of a curvilinear array of small gas bubbles ("string of beads" sign), which occurs from air collecting between the valvulae conniventes floating in a fluid-filled bowel, is pathognomonic for SBO [61]. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Plain radiography'.)

It is reasonable to not obtain plain radiographs if CT will be performed regardless, especially if the patient does not have clinical signs of bowel ischemia or perforation and has not had prior CT imaging showing obstruction. Obtaining radiographs may prolong the ED evaluation. Additionally, abdominal radiographs are in the higher range of average effective radiation dose compared with plain radiographs of other areas (eg, chest) [69].

●Additional imaging in most patients: Abdominopelvic CT – IV-contrast enhanced abdominopelvic CT is needed in most patients to further characterize the nature, severity, and potential etiologies of the obstruction (image 16 and image 17). CT without contrast enhancement can possibly diagnose SBO. In a patient with suspected partial or intermittent SBO, the surgeon may request an oral and IV contrast-enhanced CT since the presence or absence of contrast distal to the site of suspected obstruction helps guide management. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Abdominal CT'.)

However, in a patient with plain radiographs confirming obstruction, a CT may not be necessary and should be obtained in discussion with the consulting surgeon. For example, plain radiographs may be sufficient in a patient with recurrent intermittent obstructions, especially if they are followed closely by a surgeon and have had multiple prior CT scans in the setting of prior obstructions that have resolved with conservative measures. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Recurrent intermittent obstruction'.)

Right upper quadrant or epigastric pain — Imaging of a patient with right upper quadrant or epigastric pain depends on the results of liver enzymes and lipase and whether the patient has had a cholecystectomy. Causes of right upper quadrant pain (table 14) and epigastric pain (table 15) often include diseases of the liver and biliary system, pancreas, and stomach and are discussed in detail separately. (See "Causes of abdominal pain in adults", section on 'Upper abdominal pain syndromes'.)

●Patient without previous cholecystectomy or with elevation of liver enzymes or lipase: Right upper quadrant ultrasound – A right upper quadrant ultrasound is the first-line study in these patients. An ultrasound can help delineate pathology within the gallbladder and liver, assess for biliary dilatation, and determine whether gallstones are the cause of acute pancreatitis. For detection of gallstones, an ultrasound is more sensitive than CT, which has a sensitivity that ranges from 55 to 80 percent and can miss gallstones that are isodense with bile. (See "Clinical manifestations and evaluation of gallstone disease in adults", section on 'Transabdominal ultrasound' and "Clinical manifestations, diagnosis, and natural history of acute pancreatitis", section on 'Abdominal ultrasound'.)

●Patient with previous cholecystectomy and normal liver enzymes and lipase or as second-line study: Abdominal CT – An abdominal CT (IV-contrast enhanced) is the typical second-line study if the right upper quadrant ultrasound does not identify the cause of pain and the patient is felt to need further imaging (eg, high-risk features (table 1), persistent pain or tenderness, leukocytosis, pain is not consistent with gastritis). A CT can identify causes and complications of pancreatitis or a contained duodenal perforation. In general, a CT obtained for right upper quadrant pain is less likely to be abnormal compared with other indications [16]. (See "Clinical manifestations and evaluation of gallstone disease in adults", section on 'General approach'.)

Flank pain or abnormal testicular examination — A table summarizing the differential diagnosis of flank pain in an adult patient with a normal genitourinary examination is provided (table 16). An abnormal scrotal examination suggests genitourinary pathology, which can present with lower abdominal pain, flank pain, and/or hematuria. The presence of hematuria suggests renal, ureteral, or bladder pathology but may be related to non-genitourinary intrabdominal pathology, such as appendicitis. (See "Acute scrotal pain in adults: Evaluation and management of major causes" and "Evaluation of hematuria in adults".)

●Abnormal scrotal examination: Scrotal ultrasound – We obtain a scrotal ultrasound in a male with an abnormal scrotal examination to evaluate for torsion, epididymitis, hydroceles, or masses. Testicular torsion is more common in younger males but can still occur in older males, in whom an incarcerated inguinal hernia is more common. In a patient with high clinical suspicion for torsion, we consult a urologist prior to imaging confirmation. (See "Acute scrotal pain in adults: Evaluation and management of major causes".)

●Suspected nephrolithiasis: Kidney ultrasound or abdominopelvic CT – Most patients with suspected nephrolithiasis should have imaging to identify the stone and/or assess for hydronephrosis. However, renal colic can be a clinical diagnosis; thus, we may forego imaging in young patients without suspicion for a serious alternative diagnosis (eg, cholecystitis, appendicitis, AAA) or patients with recurrent stones who have been previously managed conservatively (eg, analgesia, hydration). We prefer kidney ultrasound in patients with kidney stones visualized on imaging during prior episodes, pregnant patients, and those felt to be at low risk for serious alternative diagnoses. In other patients, those with high-risk features (eg, obesity [males >129 kg, females >113 kg], kidney transplant, dialysis dependency, a solitary kidney, and age >76 years [70]), and patients with a urinalysis suggesting infection, we perform a noncontrast abdominopelvic CT. If ultrasound or CT is available, we do not perform abdominal radiography (ie, kidneys-ureters-bladder radiograph) because it has low sensitivity for detecting nephrolithiasis (72 percent for stones >5 mm but only 8 to 29 percent for a stone of any size) [71,72].

•Kidney ultrasound – An ultrasound-first approach (either emergency physician point-of-care or radiology performed) is safe and effective, and it limits cumulative radiation exposure in low-risk populations with suspected nephrolithiasis [70]. However, compared with noncontrast abdominopelvic CT, ultrasound is less accurate at identifying kidney (image 18) and ureteral calculi. In patients presenting with acute flank pain, ultrasound is nearly 100 percent sensitive for obstructive uropathy (ie, hydronephrosis (image 8), ureteral dilatation (image 19), perinephric fluid). A larger ureteral calculi (>5 mm) is less likely to be present if ultrasound does not visualize hydronephrosis, but these secondary obstructive signs of nephrolithiasis may not develop in the first two hours or with a smaller calculi [73]. Thus, a CT is sometimes performed after a negative ultrasound if a definitive diagnosis is desired, a complication (eg, infection) is suspected, the patient has unyielding pain, or if the CT is needed for treatment planning. (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Ultrasound of the kidneys and bladder'.)

•Abdominopelvic CT – A noncontrast CT reliably detects nephrolithiasis and hydronephrosis (image 20 and image 21) and can aid with spontaneous passage prognosis by assessing the stone size and location. CT can also exclude ruptured AAA, a catastrophic renal colic mimic, and thus is especially valuable in patients without prior abdominal imaging and with AAA risk factors (eg, advancing age, male sex, tobacco use, other large vessel aneurysms, family history of AAA, atherosclerosis, hypertension). If we have a high suspicion that the pain is from nephrolithiasis, we perform a noncontrast CT because contrast-enhanced parenchyma with early excretion into the pelvicalyceal system can occasionally obscure calculi within the collecting system. In other patients, performing an IV contrast-enhanced CT is reasonable since it allows for evaluating other etiologies of flank pain while preserving high sensitivity for identifying calculi large enough to be at risk of not passing spontaneously [74]. (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Noncontrast CT'.)

●Other pathology suspected (eg, renal, retroperitoneal): Abdominopelvic CT or CT urography (CTU) – In a patient who has flank pain not suspected to be from nephrolithiasis and is clinically judged to need imaging (eg, pain is not consistent with muscle strain or herpes zoster), we obtain an abdominopelvic CT (with IV contrast). This study will identify most important etiologies such as AAA, obstructive uropathy, perinephric abscess, renal infarction, and retroperitoneal hemorrhage.

A CTU is indicated in a patient with unexplained hematuria or increased risk of urinary malignancy (see "Evaluation of hematuria in adults", section on 'Risk factors for malignancy'). CTU describes an imaging acquisition protocol of the abdomen and pelvis in which noncontrast images are obtained initially, followed by IV-contrast enhanced images and delayed excretory phase imaging that opacifies the collecting system, ureters, and urinary bladder. CTU protocols vary slightly with each site, and a discussion with the radiologist is likely to be helpful to determine if the contrast-enhanced images are necessary. (See "Evaluation of hematuria in adults", section on 'Imaging studies'.)

Lower abdominal pain in female patient — Further evaluation is guided by history and findings on abdominal and pelvic examination. Examples of clinical factors that favor various etiologies of pain include the following:

●Dysuria, urinary urgency or frequency, pyuria, hematuria, vaginal or endocervical discharge, or cervical motion tenderness favors cervicitis, pelvic inflammatory disease (PID), or urinary tract infection (UTI) (see 'Suspected UTI, cervicitis, or PID' below)

●Sudden onset of sharp, severe pain with maximal intensity at onset, pelvic location of pain, vaginal bleeding, or adnexal tenderness favors gynecologic cause other than cervicitis or pelvic inflammatory disease (see 'Other gynecologic cause suspected' below)

●Migration of pain, nausea, vomiting, or anorexia favors appendicitis over a gynecologic cause [75-77] (see 'Nongynecologic cause suspected' below)

The differential diagnosis of acute pelvic pain in adult females by age group (table 17) and by clinical features (table 18) are summarized in the tables and discussed in detail separately. (See "Causes of abdominal pain in adults", section on 'Females'.)

Suspected UTI, cervicitis, or PID — A patient with a history, examination, and laboratory studies indicative of cervicitis, PID, or UTI may not need imaging and can be treated with oral antibiotics and close outpatient follow-up. Additional testing (eg, pelvic ultrasound, CT, or MRI) may be warranted for a patient who is acutely ill (eg, fever, peritonitis, hypotension), has a presentation atypical for PID or UTI (eg, abnormal site or duration of symptoms), or has not improved significantly within 72 hours after starting empiric antibiotic therapy. These findings suggest the possibility of a complication of PID (eg, tubo-ovarian abscess) or an alternate diagnosis (eg, appendicitis), which can be difficult to differentiate from PID without imaging [75]. (See "Pelvic inflammatory disease: Clinical manifestations and diagnosis" and "Acute simple cystitis in female adults".)

Other gynecologic cause suspected

●First-line: Pelvic (+/- abdominal) ultrasound – In a nonpregnant female with pelvic or lower abdominal pain whose presentation suggests a gynecologic cause of pain, we obtain a pelvic ultrasound to evaluate for ovarian torsion or ruptured ovarian cyst. If there is clinical suspicion, a concurrent abdominal ultrasound can be obtained to evaluate for appendicitis, nephrolithiasis, or a tubo-ovarian abscess. (See "Ovarian and fallopian tube torsion", section on 'Ultrasound' and "Evaluation and management of ruptured ovarian cyst", section on 'Imaging studies' and "Tubo-ovarian abscess: Epidemiology, clinical manifestations, and diagnosis", section on 'Imaging studies' and "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Ultrasound of the kidneys and bladder' and "Acute appendicitis in adults: Clinical manifestations and differential diagnosis", section on 'Ultrasound findings'.)

●Second-line: abdominopelvic CT – An abdominopelvic CT (IV-contrast enhanced) is the typical second-line study if the ultrasound does not identify the cause of pain and the patient is felt to need further imaging (eg, high-risk features (table 1), leukocytosis, persistent pain [especially if requiring multiple opioid doses], abdominal tenderness or distension).

Nongynecologic cause suspected — A nonpregnant female with a normal pelvic examination and abdominal pain concerning for a nongynecologic cause is best evaluated with an abdominopelvic CT. (See 'Other patients (eg, lower abdominal pain)' below.)

High-risk patients

Older adults — We have a low threshold to obtain imaging in older adults with abdominal or flank pain because serious abdominal pathology is more likely, misdiagnosis is common, and associated mortality is increased. The characteristic presentation of diseases provides the initial basis for assessment and imaging, even in older patients, but clinicians must remain mindful of atypical presentations of common diseases and extra-abdominal causes of pain (eg, myocardial infarction).

●Epidemiology – Older patients (ie, ≥65 years) with abdominal pain have a six- to eightfold increase in mortality compared with younger patients [9,19]. Approximately one-half to two-thirds require hospitalization, one-fifth to one-third require surgical intervention, and 5 percent die within two months [3,10,19,29,78,79]. A study of the United States National Hospital Ambulatory Medical Care Survey from 2013 to 2017 found that 3.6 percent of patients 65 years or older were admitted directly from the ED to the operating room [80].

Misdiagnosis of abdominal pain is common in older adults, especially in those ≥75 years, and associated with higher mortality compared with younger patients [19,81].

●Atypical presentations – Older patients are more likely to have symptoms of disease that are not characteristic compared with younger individuals (ie, "atypical" symptoms) and clinical presentations that underestimate the severity of disease, such as not mounting a fever or tachycardia in response to infection or inflammation [79,82,83]. Older patients are more likely to take medications, such as beta-blockers and glucocorticoids, and have comorbidities such as diabetes that can mask characteristic symptoms and signs.

As examples, older adults with a perforated ulcer can present without the typical sudden onset of pain [17]. Older adults with appendicitis often present without characteristic findings (eg, pain migration) and are less likely to have a leukocytosis [17,84-86]. Older adults with an intra-abdominal infection are four times more likely than younger patients to present with hypothermia [10].

Biliary tract disease is among the most common causes of abdominal pain in older adults but also frequently presents without characteristic abdominal pain or tenderness. Older adults diagnosed surgically with cholecystitis presented more often with nausea or vomiting instead of pain; 84 percent had neither epigastric nor right upper quadrant pain [83]. A Murphy sign may not be present, and liver enzymes are less frequently abnormal in older adults with cholecystitis [87-89].

●Physical examination differences – Physical examination cannot reliably predict or exclude significant disease in older adults [29]. In a study of hospitalized older adults with peritonitis, only 34 percent manifested guarding or rebound tenderness [30]. With increasing age, the loss of spinal afferent innervation can limit hollow viscous and peritoneal nociception [90,91].

Malignancy — We have a low threshold to obtain imaging in a patient with an active malignancy and abdominal or flank pain. Chemotherapy and radiation therapy themselves can produce abdominal pain, but this should be a diagnosis of exclusion. For example, vincristine can cause severe, colicky abdominal pain for up to 10 days after administration. However, serious pathology is also possible, such as neutropenic enterocolitis (typhlitis), which typically occurs during the neutrophil count nadir in a patient receiving chemotherapy for leukemia. (See "Clinical presentation and risk factors for chemotherapy-associated diarrhea, constipation, and intestinal perforation" and "Neutropenic enterocolitis (typhlitis)".)

HIV infection — The diagnostic evaluation of abdominal and flank pain in the adult with human immunodeficiency virus (HIV) is similar to adults without HIV but is also guided by immunologic function based on the CD4 cell count and the presence of antiretroviral medications. We have a low threshold to obtain imaging in a patient with advanced immunodeficiency (CD4 cell count <100 cells/microL). Of HIV-positive patients presenting with abdominal pain, 38 percent will require admission [92]. The differential diagnosis includes common etiologies (eg, appendicitis, diverticulitis, undifferentiated abdominal pain) but there is also an elevated risk of medication induced pancreatitis, multiple opportunistic infections (eg, cytomegalovirus [CMV], Mycobacterium avium complex [MAC], cryptosporidium) and neoplasms (eg, Kaposi sarcoma, lymphoma) [92,93]. Additionally, some protease inhibitors (eg, atazanavir) can cause radiolucent kidney stones that are not visualized on CT. (See "AIDS-related cytomegalovirus gastrointestinal disease" and "Mycobacterium avium complex (MAC) infections in persons with HIV" and "Cryptosporidiosis: Epidemiology, clinical manifestations, and diagnosis" and "AIDS-related Kaposi sarcoma: Clinical manifestations and diagnosis" and "HIV-related lymphomas: Clinical manifestations and diagnosis" and "Crystalline-induced acute kidney injury", section on 'Protease inhibitors'.)

Sickle cell disease — We have a low threshold to obtain imaging if the abdominal or flank pain is not typical of previous pain episodes. A patient with sickle cell disease can have intermittent abdominal pain as part of a vaso-occlusive episode but is also at increased risk of having gallstones, cholecystitis, acute hepatic sequestration, acute splenic sequestration, renal papillary necrosis, UTI, pyelonephritis, or opioid-induced constipation. (See "Evaluation of acute pain in sickle cell disease", section on 'Abdominal pain' and "Hepatic manifestations of sickle cell disease".)

Organ transplant recipient — An organ transplant recipient with abdominal or flank pain often requires imaging (eg, CT, MRI) because transplanted organs are denervated and lose normal lymphatic drainage and thus do not have characteristic manifestations of pathology. Additionally, immunosuppressive agents can mask signs and symptoms of peritonitis or systemic infection. Common and opportunistic abdominal infections can develop, such as cytomegalovirus colitis, hepatitis B and C viral infections, gastrointestinal parasites (eg, Cryptosporidium and Microsporidium), and UTIs, particularly in kidney transplant recipients. Post-surgical undrained fluid collections or blockage or leaks of anastomoses can cause pain or become infected. Acute kidney rejection can present with allograft pain and tenderness. Kidney transplant recipients with pain and tenderness over their kidney allograft, and selected patients diagnosed with a UTI should have an ultrasound of the allograft. (See "Urinary tract infection in kidney transplant recipients", section on 'Imaging/urologic evaluation in selected patients' and "Infection in the solid organ transplant recipient" and "Kidney transplantation in adults: Evaluation and diagnosis of acute kidney allograft dysfunction".)

Immunosuppressive agents increase risk of various malignancies that can present with abdominal or flank pain. For example, kidney transplant recipients are at increased risk of renal cell carcinoma, anogenital cancers, and post-transplant lymphoproliferative disorders that can cause abdominal pain if extranodal masses arise in the stomach or intestine. (See "Overview of care of the adult kidney transplant recipient", section on 'Malignancy' and "Epidemiology, clinical manifestations, and diagnosis of post-transplant lymphoproliferative disorders".)

Bariatric surgery — Many complications of bariatric surgery cause abdominal pain and can present weeks, months, or years after the surgery. A contrast-enhanced (often both IV and oral) abdominopelvic CT is typically necessary, but imaging decisions should be made in consultation with the patient's bariatric surgeon. Imaging with CT is essentially required if the surgeon cannot be reached or the specifics of the procedure are unavailable (eg, surgery performed internationally). Some patients will need endoscopy or laparoscopic exploration even if the CT is normal. In addition to bowel obstruction, other potential complications include (see "Metabolic and bariatric operations: Early morbidity and mortality" and "Bariatric operations: Late complications with acute presentations" and "Bariatric operations: Late complications with subacute presentations") [94-96]:

●Roux-en-Y gastric bypass – Gastric remnant distension, stomal stenosis, marginal ulceration

●Gastric banding – Stomal obstruction, port infection, band erosion or movement

●Sleeve gastrectomy – Gastric leaks, gastric outlet syndrome

Other patients (eg, lower abdominal pain) — In a patient with abdominal or flank pain who does not fit into any of the above categories, the decision to image and choice of study differs based on the patient's sex, age, and location of pain. In general, we obtain imaging in a patient with high-risk features (table 1), leukocytosis or other laboratory abnormalities, persistent pain (especially if requiring multiple opioid doses), abdominal tenderness or distension; and at a surgeon’s request. In a patient with no indications for imaging, further management is based on shared decision-making and may include discharge with clear ED return precautions or observation for serial abdominal examinations.

The differential diagnoses of lower abdominal pain (table 19), diffuse abdominal pain (table 20), and left upper quadrant pain (table 21) are provided in the tables and discussed in detail separately. (See "Causes of abdominal pain in adults", section on 'Lower abdominal pain syndromes' and "Causes of abdominal pain in adults", section on 'Diffuse abdominal pain syndromes' and "Causes of abdominal pain in adults", section on 'Left upper quadrant pain'.)

In a young male patient with a high clinical suspicion for appendicitis (right lower quadrant abdominal pain and tenderness, anorexia, nausea/vomiting, leukocytosis, modified Alvarado score ≥4 (table 22)), we obtain surgical consultation prior to imaging. The surgeon may request imaging based on clinical suspicion and the local acceptable nontherapeutic operative rate. (See "Acute appendicitis in adults: Diagnostic evaluation".)

Mesenteric lymphadenitis (ie, inflammation of the mesenteric lymph nodes) is a common benign cause of nonspecific abdominal pain but can mimic appendicitis [97]. It is a diagnosis of exclusion in the ED and can often be identified by the presence of enlarged lymph nodes on abdominopelvic CT or abdominal ultrasound (the latter may not be sufficient to exclude appendicitis). Causes include viral infections (the most common), bacterial infections (eg, gastroenteritis), inflammatory bowel disease, and lymphoma. If caused by a viral infection, the course is self-limited, resolving within several weeks. (See "Causes of acute abdominal pain in children and adolescents", section on 'Mesenteric lymphadenitis'.)

●First-line: Abdominopelvic CT – In a male or nonpregnant female with suspected nongynecologic etiology with lower abdominal (especially right lower quadrant), left upper quadrant, or diffuse abdominal pain, an IV contrast-enhanced abdominopelvic CT is the study with the best accuracy. Even in the absence of IV contrast, CT is still helpful to diagnose appendicitis and other conditions since inflammatory changes in mesenteric fat are a secondary finding in many processes (eg, pericecal and periappendiceal fat in case of appendicitis). However, such inflammatory changes can be obscured in young, slender patients with little retroperitoneal and mesenteric fat. We do not routinely administer oral contrast, which is discussed further above. (See 'Overview of common imaging modalities' above.)

In a patient with left lower quadrant pain, an IV contrast-enhanced abdominopelvic CT is the most accurate modality to diagnose diverticulitis [98]. While CT is not necessary for all patients with suspected diverticulitis, it is helpful to confirm the diagnosis in a patient without a previous history of diverticular disease and to assess for complications (eg, perforation, abscess formation) in a patient with known disease but severe symptoms. When symptoms are consistent with prior diverticulitis episodes, we will use shared decision-making regarding treatment and reassessment versus immediate imaging. (See "Clinical manifestations and diagnosis of acute colonic diverticulitis in adults", section on 'Diagnostic approach'.)

●Alternative imaging options

•Abdominal ultrasound – An abdominal ultrasound, if used for the appropriate indication, is an alternative imaging option that avoids exposing the patient to ionizing radiation or IV contrast. It can evaluate the aorta, liver, spleen, biliary tract, pregnancy, reproductive organs, bladder, kidneys, and appendix but is not typically helpful in evaluating bowel pathology.

When used to diagnose appendicitis, test performance is variable and depends on patient-specific (eg, body habitus, discomfort and alertness, appendix location relative to overlying bowel) and operator-specific (eg, experience) variables. Ultrasound has a reported sensitivity of approximately 85 percent and a specificity of 90 percent. Rates of indeterminate examinations are high, with 50 to 85 percent of normal appendices not visualized. (See "Acute appendicitis in adults: Diagnostic evaluation", section on 'Ultrasound'.)

•MRI – MRI is an accurate alternative to CT for excluding intra-abdominal pathology (eg, appendicitis) when trying to avoid radiation exposure or administering CT contrast. Use of MRI to diagnose appendicitis is discussed separately. (See "Acute appendicitis in adults: Diagnostic evaluation", section on 'Magnetic resonance imaging'.)

ANALGESIA — 

We offer the patient targeted analgesia to facilitate the emergency department (ED) evaluation. The goal of analgesia is to reduce the pain to manageable levels, improve patient comfort, and possibly improve the accuracy of the abdominal examination by minimizing voluntary guarding. The goal is not to eliminate all pain or make the patient somnolent.

Non-opioid therapy is often preferable to minimize opioid use and avoid adverse effects. Common options include the following:

●Acetaminophen – This is helpful as part of multimodal analgesia for all patients with acute pain and without contraindications, such as severe hepatic insufficiency or active liver disease. It can also be administered intravenously (IV) to patients who cannot take oral medications. (See "Nonopioid pharmacotherapy for acute pain in adults", section on 'Acetaminophen'.)

●Nonsteroidal anti-inflammatory drugs (NSAIDs) – Parenteral ketorolac is a first-line analgesic for renal colic. NSAIDs, including ketorolac, can be helpful for acute abdominal pain in many other circumstances but should be used cautiously since they can exacerbate gastritis, peptic ulcer disease, and acute kidney injury. (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis", section on 'Pain control' and "Nonopioid pharmacotherapy for acute pain in adults", section on 'Nonsteroidal anti-inflammatory drugs'.)

●Antacids – These usually contain a combination of magnesium hydroxide, aluminum hydroxide, or calcium carbonate and can rapidly relieve pain from gastroesophageal reflux disease. The "GI cocktail" commonly used in the ED is a mixture of viscous lidocaine, an antacid (eg, Maalox), and occasionally an anticholinergic agent (eg, Donnatal). However, pain improvement after an antacid is nondiagnostic since pain from biliary colic and acute coronary syndrome can resolve spontaneously, but the relief may be attributed to the effects of the antacid [99]. (See "Antiulcer medications: Mechanism of action, pharmacology, and side effects", section on 'Antacids'.)

When feasible, non-pharmacologic treatment of abdominal pain should be offered, such as application of heat to the lower abdomen for relief of dysmenorrhea. (See "Dysmenorrhea in adult females: Treatment", section on 'Heat'.)

Opioid analgesia may be required for a patient with severe pain or pain that does not improve with these measures. Morphine, hydromorphone, or fentanyl (which is preferable when shorter duration or fewer hemodynamic effects are desired) are reasonable choices when an opioid is felt to be necessary. We give opioids in intermittent doses titrated to effect with close monitoring of respiration.

Multiple trials have disproved the notion that analgesia interferes with the assessment of abdominal pain [100-104]. Opioids can alter the physical examination of patients with acute abdominal pain, but they do not result in more frequent incorrect management decisions [103].

Alternative, less frequently used options for analgesia include the following:

●First-generation antipsychotic agents – In a patient with recalcitrant pain, especially associated with vomiting or the cannabis hyperemesis syndrome, droperidol (0.625 or 1.25 mg) or haloperidol (0.05 to 0.1 mg/kg, maximum single dose 2.5 mg) is often helpful. (See "Cannabinoid hyperemesis syndrome".)

●Ketamine – A small trial of adults with primarily nontraumatic abdominal or flank pain found that a nondissociative dose of ketamine (0.3 mg/kg) produced comparable analgesia to morphine (0.1 mg/kg) without serious adverse events [105]. A trial with 200 patients with renal colic found that ketamine 0.2 mg/kg combined with morphine 0.1 mg/kg, compared with morphine alone, reduced pain severity, need for redosing, and vomiting [106]. Ketamine can alternatively be nebulized, which may be as effective as intravenous administration for pain management. A trial with 150 patients with acute pain (102 patients with abdominal or flank pain) found that ketamine 0.75 mg/kg via breath-actuated nebulizer, compared with ketamine 0.3 mg/kg IV, produced a similar reduction in pain scores without serious adverse events [107]. (See "Nonopioid pharmacotherapy for acute pain in adults", section on 'Ketamine'.)

●Morphine with patient-controlled analgesia (PCA) – Although not used routinely, several trials of ED patients with nontraumatic abdominal pain have found that morphine PCA produced greater reductions in pain and no differences in adverse events when compared with standard management using the same medication [108,109].

The Guidelines for Reasonable and Appropriate Care in the Emergency Department 2 (GRACE-2) recommend an opioid-minimizing approach for analgesia in patients with low-risk, recurrent, undifferentiated abdominal pain [110]. The GRACE-2 definition of recurrent pain is two or more prior similar episodes within 12 months, with the time elapsed from the first episode to the current episode being greater than 30 days. Patients with the following characteristics were excluded from the low-risk category:

•Unstable vital signs

•History and physical examination findings suggesting acute abdominal pathology

•Age <18 years or ≥65 years

•Pregnancy

•Acute trauma within seven days

•Organ transplantation

•Immunosuppression

•Abdominal surgery within 30 days

•Active cancer

•Inflammatory bowel disease

•Previous bowel obstruction

•Severe active psychiatric illness

DISPOSITION — 

In a patient whose cause of pain is identified, the disposition is relatively straightforward and based on management of the specific etiology. However, in a patient with an unrevealing evaluation, the disposition depends upon age, comorbidities, extent of pain, need for pain management, whether imaging was performed, certainty of imaging results, likelihood of serious disease, availability of expedited follow-up care, and reliability and social supports. This generally involves shared decision-making with the patient.

Less common causes of abdominal pain (table 23), many of which are not typically diagnosed during an emergency department (ED) visit, are discussed separately. (See "Causes of abdominal pain in adults", section on 'Less common causes'.)

●Patient with normal cross-sectional imaging (computed tomography [CT] or magnetic resonance imaging [MRI]) and laboratory results – We will reassure and discharge most patients with nonspecific abdominal or flank pain, even older adults, who have normal cross-sectional imaging and laboratory results. A normal abdominopelvic CT increases physician comfort with not identifying a specific cause for the abdominal pain and with discharging a patient who might otherwise be admitted for observation [111]. Discharged patients must be provided with clear, written instructions of potential danger signs and where and when to return for emergency care or re-evaluation. One common approach is to instruct the patient to follow up for re-evaluation with their primary care clinician in 12 to 48 hours or to return to the ED if they cannot not be seen by their outpatient clinician in that timeframe.

After an appropriate ED evaluation, most patients with a diagnosis of nonspecific abdominal pain have a benign condition that resolves without further intervention [8,112,113]. For example, in a study of 1411 patients discharged from the ED with nonspecific abdominal pain, 112 patients (8 percent) returned to the ED with abdominal pain [114]. Of these, 85 patients were again diagnosed with nonspecific pain while 17 (1 percent) had an operation, eight were diagnosed with cholelithiasis, five with appendicitis, and two with gastrointestinal cancer.

●Patient with continued concern for serious pathology despite normal imaging – If there remains doubt about the nature or seriousness of the underlying cause, especially in older adults or those with comorbidities, we will admit to the hospital or observe the patient for a prolonged period (eg, at least 6 to 12 hours) in the ED. In a patient with abdominal pain of unclear etiology, observation and reassessment can often determine the cause or exclude serious pathology. For example, several studies found that a period of observation increased the diagnostic accuracy for appendicitis [24,115].

●Patient with uncontrolled pain – It can be challenging to determine the disposition of a patient who is requiring multiple intravenous (IV) opioid doses for pain management without a specific diagnosis identified after a thorough ED evaluation. Guidelines suggest an opioid-minimizing approach for analgesia in patients with low-risk, recurrent, undifferentiated abdominal pain [110]. We suggest having a discussion with the patient regarding the risks of continued opioid therapy versus their limited benefit prior to making the decision to admit for pain control or discharging with a prescription for oral opioids. (See 'Analgesia' above and "Evaluation of the adult with abdominal pain", section on 'Diagnostic approach to chronic abdominal pain' and "Use of opioids in the management of chronic pain in adults", section on 'Indications for opioid therapy'.)

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Nontraumatic abdominal pain in adults".)

INFORMATION FOR PATIENTS — 

UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)

●Basics topic (see "Patient education: Abdominal pain (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Initial evaluation – The evaluation of an adult emergency department (ED) patient with abdominal or flank pain starts with obtaining a history, performing a physical examination, and rapidly assessing if the patient may have an abdominal catastrophe (clues include hypotension or other signs of shock, peritonitis, toxic appearance). High-risk features of abdominal pain must be appreciated (table 1). (See 'Overview of the evaluation' above.)

●History – The quality, timing, and location of pain help determine the acuity and focus the differential diagnosis (table 2 and figure 1 and table 3 and table 16). Pain that is severe and maximum intensity at onset is concerning for a vascular emergency (eg, aortic rupture or dissection, mesenteric ischemia, pulmonary embolism), obstruction of a small tubular structure (eg, ureter), or reproductive organ pathology (eg, ovarian torsion, ruptured ovarian cyst). The presence of associated symptoms (table 6), pre-existing medical and surgical conditions, medications, and social history (table 7) increases a patient's risk for various diseases. (See 'History' above.)

●Physical examination – Abdominal palpation localizes the tenderness and detects signs of peritoneal irritation, such as involuntary guarding and muscular rigidity. A rigid abdomen is cause for concern, but traditional techniques for assessing rebound tenderness have limited sensitivity and specificity for identifying peritonitis. (See 'Physical examination' above.)

●Role of point-of-care ultrasound – Emergency physician-performed point-of-care ultrasound has become an important tool for the evaluation of patients with abdominal pain. Ultrasound is especially helpful in the unstable patient or when there is concern for abdominal catastrophe. It can identify hemoperitoneum, abdominal aortic aneurysm (AAA), intrauterine pregnancy, gallstones, a distended urinary bladder, pericardial effusion, and hydronephrosis and measure inferior vena cava diameter as an indicator of fluids status. (See 'Role of point-of-care ultrasound' above.)

●Ancillary studies – Unless the history and physical examination establish the cause of pain, most patients will need laboratory studies, which are discussed in the text. (See 'Ancillary studies' above.)

●Patient with suspected abdominal catastrophe – Abdominal processes that can cause ischemia, sepsis, or hemorrhage and become a life-threatening abdominal catastrophe are presented in the table (table 10). An approach in a pregnant patient with hemodynamic instability or peritonitis is presented in the algorithm (algorithm 2). (See 'Differential diagnosis of abdominal catastrophe' above.)

Start treatment simultaneously with the initial evaluation when there is a concern for an abdominal catastrophe. Establish venous access, start intravenous (IV) fluids (ie, crystalloid), obtain laboratory studies, and perform point-of-care ultrasound. Patients may need vasopressors, stress-dose glucocorticoids, blood product transfusion, and/or empiric broad-spectrum antibiotics. (See 'Resuscitation' above.)

We consult procedural specialists early in the patient's ED course since surgical intervention and/or percutaneous drainage are usually necessary to obtain source control of intra-abdominal infections or to obtain hemostasis of intraperitoneal hemorrhage. (See 'Specialty consultation' above.)

Obtain a portable upright chest radiograph (CXR) since the presence of pneumoperitoneum confirms the diagnosis of hollow viscous perforation. Abdominopelvic computed tomography (CT) is the preferred study in a patient with a suspected abdominal catastrophe and undifferentiated abdominal. (See 'Imaging' above.)

●Patient without abdominal catastrophe – Further evaluation depends on the patient's pregnancy status. The approach to acute abdominal or pelvic pain in a hemodynamically stable pregnant patient without peritonitis is provided in the algorithm (algorithm 4) and discussed in detail separately. (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients", section on 'Acute abdominal pain related to pregnancy or the reproductive tract'.)

The evaluation of the adult male and nonpregnant female is provided in the algorithm (algorithm 1) and discussed further in the text. (See 'Cause not identified by history and physical' above.)

Further testing can sometimes be deferred or avoided when the history, examination, and laboratory studies (if performed) identify a clear etiology. Example scenarios are provided in the text. (See 'Cause identified by history and physical' above.)

●High-risk conditions – Risk factors for serious causes of abdominal and flank pain include older age, immunocompromise, human immunodeficiency virus (HIV) infection, active malignancy, taking chronic glucocorticoids or immunosuppressants, alcohol misuse, recipient of an organ transplant, sickle cell disease, prior abdominal (especially bariatric) surgeries, cardiovascular disease, and recent instrumentation. (See 'High-risk patients' above.)

●Analgesia – We offer the patient targeted analgesia to facilitate the ED evaluation. Analgesics, including opioids, do not interfere with the assessment of abdominal pain and do not result in more frequent incorrect management decisions. The goal of analgesia is to reduce pain to manageable levels, improve patient comfort, and possibly improve the accuracy of the examination by minimizing voluntary guarding. The goal is not to eliminate all pain. We minimize opioid administration in patients with low-risk, recurrent, undifferentiated abdominal pain. (See 'Analgesia' above.)

●Disposition – In a patient who does not have a specific etiology identified, the disposition depends upon age, comorbidities, extent of pain, need for pain management, whether imaging was performed, certainty of imaging results, likelihood of serious disease, availability of expedited follow-up care, and reliability and social supports. We will reassure and discharge most patients with nonspecific abdominal pain, even older adults, who have a normal CT and laboratory results. If there remains doubt about the nature or seriousness of the underlying cause, especially in older adults or those with high-risk conditions, we will admit to the hospital or observe the patient in the ED. (See 'Disposition' above.)