Approach to acute lower gastrointestinal bleeding in adults

INTRODUCTION — Acute lower gastrointestinal (GI) bleeding refers to blood loss of recent onset originating from the colon. The causes of acute lower GI bleeding may be grouped into several categories: anatomic (diverticulosis), vascular (angiodysplasia, ischemic, radiation-induced), inflammatory (infectious, inflammatory bowel disease), and neoplastic. In addition, acute lower GI bleeding can occur after therapeutic interventions such as polypectomy. (See "Etiology of lower gastrointestinal bleeding in adults" and "Management and prevention of bleeding after colonoscopy with polypectomy".)

This topic will review the clinical manifestations, diagnosis, and initial management of acute GI bleeding thought to be coming from the colon. The etiology of lower GI bleeding and the treatment of specific causes of bleeding, as well as approaches to patients with upper GI bleeding, minimal rectal bleeding, suspected small bowel bleeding, and occult GI bleeding, are discussed separately. (See "Etiology of lower gastrointestinal bleeding in adults" and "Colonic diverticular bleeding" and "Angiodysplasia of the gastrointestinal tract" and "Management and prevention of bleeding after colonoscopy with polypectomy" and "Approach to acute upper gastrointestinal bleeding in adults" and "Approach to minimal bright red blood per rectum in adults" and "Evaluation of suspected small bowel bleeding (formerly obscure gastrointestinal bleeding)" and "Evaluation of occult gastrointestinal bleeding".)

OVERVIEW — Patients with acute lower gastrointestinal (GI) bleeding typically present with hematochezia, although hematochezia may also be seen in patients with massive upper GI or small bowel bleeding. Rarely, patients with right-sided colonic bleeding will present with melena. The bleeding will stop spontaneously in 80 to 85 percent of patients, and the mortality rate is 2 to 4 percent [1]. (See 'Clinical manifestations' below.)

In patients suspected of having acute lower GI bleeding, the approach to diagnosis and management includes (algorithm 1):

●General management, including obtaining adequate intravenous access, triaging the patient to the appropriate level of care, and providing supportive measures such as supplemental oxygen (see 'Initial evaluation and management' below)

●Resuscitation, which should occur in parallel with the diagnostic evaluation (see 'Fluid resuscitation' below and 'Blood transfusions' below)

●Exclusion of acute upper GI bleeding with upper endoscopy if indicated (eg, in a patient with massive hematochezia and signs of hemodynamic compromise) (see 'Consider an upper GI bleeding source' below)

●Evaluation for a lower GI source of the bleeding, typically with colonoscopy (see 'Diagnostic studies' below)

The approach to subsequent treatment depends on the source of the bleeding. If bleeding or stigmata of recent hemorrhage are identified during colonoscopy or angiography, attempts can be made to control the bleeding. However, frequently, active bleeding is not seen, and a presumptive diagnosis is made regarding the source of the bleeding (eg, diverticular bleeding in a patient with diverticula and no other potential sources). In those cases, the management approach will vary depending on the type of lesion (eg, endoscopic treatment is appropriate for angiodysplasia, but not for nonbleeding diverticula). If no source is identified the patient may need to be evaluated for upper and mid-GI bleeding. (See "Angiodysplasia of the gastrointestinal tract", section on 'Nonbleeding angiodysplasias in patients with GI bleeding' and "Colonic diverticular bleeding", section on 'Endoscopic therapy in hemodynamically stable patients' and "Management and prevention of bleeding after colonoscopy with polypectomy", section on 'Management'.)

CLINICAL MANIFESTATIONS — A patient with lower gastrointestinal (GI) bleeding typically reports hematochezia (passage of maroon or bright red blood or blood clots per rectum). Blood originating from the left colon tends to be bright red in color, whereas bleeding from the right side of the colon usually appears dark or maroon colored and may be mixed with stool. Rarely, bleeding from the right side of the colon will present with melena.

The initial hemoglobin in patients with acute lower GI bleeding will typically be at the patient's baseline because the patient is losing whole blood. With time (typically after 24 hours or more), the hemoglobin will decline as the blood is diluted by the influx of extravascular fluid into the vascular space and by fluid administered during resuscitation. It should be kept in mind that overhydration can lead to a falsely low hemoglobin value.

Patients with acute bleeding should have normocytic red blood cells. Microcytic red blood cells or iron deficiency anemia suggest chronic bleeding. Unlike patients with acute upper GI bleeding, patients with acute lower GI bleeding and normal renal perfusion should have a normal blood urea nitrogen (BUN)-to-creatinine or urea-to-creatinine ratio (<20:1 or <100:1, respectively) [2].

INITIAL EVALUATION AND MANAGEMENT — The initial evaluation and management of a patient with suspected acute lower gastrointestinal (GI) bleeding should occur in parallel. The goals are to determine if the bleeding is coming from the lower GI tract, determine the severity of bleeding, triage patients to the appropriate setting, provide general supportive measures, and to initiate resuscitation. Once these steps are complete, additional diagnostic studies (eg, colonoscopy) can be obtained (algorithm 1). Our approach to the management of lower GI bleeding is largely consistent with guidelines from the American College of Gastroenterology and the British Society of Gastroenterology [3]. (See 'Diagnostic studies' below.)

Initial evaluation — The initial evaluation includes a history, physical examination, laboratory tests, and in some cases, upper endoscopy. The goal of the evaluation is to assess the severity of the bleeding, assess whether the bleeding may be coming from the upper GI tract, and determine if there are conditions present that may affect subsequent management.  

History — Patients should be asked about prior episodes of GI bleeding, and the patient's past medical history should be reviewed to identify potential bleeding sources and to identify comorbidities that may influence the patient's subsequent management. Patients should be asked about medication use, particularly agents that are associated with bleeding or that may impair coagulation, such as nonsteroidal antiinflammatory agents, anticoagulants, and antiplatelet agents. Patients should also be asked about symptoms that may suggest a particular etiology for the bleeding (eg, painless hematochezia with diverticular bleeding, change in bowel habits with malignancy, abdominal pain with colitis). (See "Etiology of lower gastrointestinal bleeding in adults".)

Physical examination — The physical examination should include an assessment of hemodynamic stability as well as examination of the patient's stool to confirm the presence of hematochezia or melena. (See 'Clinical manifestations' above.)

Signs of hypovolemia include [4]:

●Mild to moderate hypovolemia: Resting tachycardia

●Blood volume loss of at least 15 percent: Orthostatic hypotension (a decrease in the systolic blood pressure of more than 20 mmHg or decrease in diastolic pressure of more than 10 mmHg when moving from recumbency to standing)

●Blood volume loss of at least 40 percent: Supine hypotension

The presence of abdominal pain suggests the presence of an inflammatory bleeding source such as ischemic or infectious colitis or a perforation (eg, a perforated peptic ulcer in a patient with severe upper GI bleeding).

Laboratory tests — Laboratory tests that should be obtained in patients with acute GI bleeding include a complete blood count, serum chemistries, liver tests, and coagulation studies. The initial hemoglobin level should be monitored every two to twelve hours, depending on the severity of the bleed. In the setting of acute lower GI bleeding, patients' hemoglobin values should be at their baseline, with normocytic red blood cell (RBC) indices (provided the patient did not have preexisting anemia). (See 'Clinical manifestations' above.)

Consider an upper GI bleeding source — The primary consideration in the differential diagnosis of hematochezia is upper GI bleeding since 10 to 15 percent of patients with severe hematochezia will have an upper GI source [1]. Findings that are suggestive of an upper GI source include hemodynamic instability, orthostatic hypotension, and an elevated blood urea nitrogen (BUN)-to-creatinine or urea-to-creatinine ratio (>20 to 30:1 or >100:1, respectively) [2,5-11]. A preceding history of prior peptic ulcer disease may suggest the possibility of an upper GI source of bleeding. On the other hand, blood clots in the stool decrease the likelihood of an upper GI source [11].

If the index of suspicion for an upper GI source is high, an upper endoscopy should be performed once the patient is appropriately resuscitated. (See 'Initial management' below.)

Initial management — The initial management of a patient with suspected acute lower GI bleeding includes triage to the appropriate setting for management (outpatient, inpatient, intensive care unit), general supportive measures (eg, oxygen, establishment of adequate intravenous access), appropriate fluid and blood product resuscitation, and management of coagulopathies, anticoagulants, and antiplatelet agents.

Triage and consultations — Visible rectal bleeding occurring in adults warrants an evaluation in all cases [12,13]. The timing and setting of the evaluation depend upon the severity of bleeding and the patient's comorbid illnesses. A gastroenterology consultation should be obtained early in the hospital course of patients with acute lower GI bleeding. General surgery and interventional radiology should also be involved in cases of massive hematochezia or those who are at high risk for complications.

Patients with high-risk features including hemodynamic instability (shock, orthostatic hypotension), persistent bleeding, and/or significant comorbid illnesses should be admitted to an intensive care unit for resuscitation, close observation, and possible therapeutic interventions. Close observation includes automated blood pressure monitoring, electrocardiogram monitoring, and pulse oximetry. Most other patients can be admitted to a regular medical ward. We suggest that all patients admitted to a regular medical ward receive electrocardiogram monitoring.

Several studies have identified clinical features that predict the risk of complications in patients with presumed acute lower GI bleeding. These features can be used to help categorize patients as either low or high risk [14-18]. High-risk features include:

●Hemodynamic instability (hypotension, tachycardia, orthostasis, syncope)

●Persistent bleeding

●Significant comorbid illnesses

●Advanced age

●Bleeding that occurs in a patient who is hospitalized for another reason

●A prior history of bleeding from diverticulosis or angiodysplasia

●Current aspirin use

●Prolonged prothrombin time

●Hypoalbuminemia

●A non-tender abdomen

●No diarrhea

●Anemia

●An elevated blood urea nitrogen level

●An abnormal white blood cell count

The number of high-risk features present correlates with the likelihood of a poor outcome [16,18,19].

The shock index (heart rate/systolic blood pressure) is a tool to identify unstable patients with GI bleeding [3]. Patients with an index of >1 may be considered for initial evaluation with a computed tomography (CT) angiography.

Outpatient management may be appropriate for some low-risk patients (eg, a young, otherwise healthy patient with minor, self-limited rectal bleeding and no hemodynamic compromise) [20]. Risk stratification tools can be used to supplement clinical judgment to help identify low-risk patients [21]. The extent of evaluation (flexible sigmoidoscopy versus colonoscopy) in these patients depends, at least in part, upon the patient's age [22]. A large study in 143 hospitals in the United Kingdom identified patients with acute lower GI bleeding who could be safely managed without hospital admission. Age, sex, prior history of lower GI bleeding, presence of blood on rectal exam, heart rate, systolic blood pressure, and hemoglobin concentration were the features used to determine safe discharge. A score of ≤8 predicted a 95 percent probability of safe discharge [19]. In a separate validation study, an Oakland Score threshold of 8 points or lower had a sensitivity and specificity for safe discharge of 98 and 16 percent, respectively [23]. (See "Approach to minimal bright red blood per rectum in adults", section on 'Clinical assessment'.)

General supportive measures — Patients should receive supplemental oxygen by nasal cannula and initially should receive nothing per mouth in the event urgent upper endoscopy is needed. Two large caliber (18 gauge or larger) peripheral intravenous catheters or a central venous line should be inserted for intravenous access, and placement of a pulmonary artery catheter should be considered in patients with hemodynamic instability or who need close monitoring during resuscitation, such as those with heart failure or valvular disease. (See "Pulmonary artery catheterization: Indications, contraindications, and complications in adults".)

Fluid resuscitation — Adequate resuscitation and stabilization is essential in patients with acute GI bleeding [24]. Patients with active bleeding should receive intravenous fluids (eg, 500 mL of normal saline or lactated Ringer's solution over 30 minutes) while being typed and cross-matched for blood transfusion. Patients at risk of fluid overload may require intensive monitoring with a pulmonary artery catheter. If the blood pressure fails to respond to initial resuscitation efforts, the rate of fluid administration should be increased and urgent intervention (eg, angiography) considered. (See 'Angiography' below.)

Blood transfusions — Review of pertinent laboratory data is an essential step during resuscitation to assess the need for blood product transfusion. The decision to initiate blood transfusions must be individualized, and specific thresholds for transfusion have not been delineated. Hemodynamically stable patients without comorbid illness may not require transfusion until the hemoglobin falls below 7 g/dL (70 g/L) [20,21,25]. On the other hand, older patients and those who have severe comorbid illnesses, such as active coronary disease, require packed RBC transfusions to maintain a higher hemoglobin level (eg, 9 to 10 g/dL [90 to 100 g/L]) [20,26]. We do not have an age cutoff for determining which patients should have a goal hemoglobin of ≥9 g/dL, and instead base the decision on the patient's comorbid conditions. In addition, patients with active bleeding and hypovolemia may require a blood transfusion despite apparently normal hemoglobin. (See "Practical aspects of red blood cell transfusion in adults: Storage, processing, modifications, and infusion".)

Studies in patients with acute upper GI bleeding suggest that using a lower hemoglobin threshold is associated with improved outcomes. (See "Approach to acute upper gastrointestinal bleeding in adults", section on 'Blood product transfusions'.)

Management of coagulopathies, anticoagulants, and antiplatelet agents — Decisions regarding the management of anticoagulants and antiplatelet agents in patients with acute lower GI bleeding should be individualized. Typically, in patients with life-threatening bleeding and a coagulopathy (prolonged prothrombin time with international normalized ratio [INR] greater than 1.5), warfarin and direct-acting anticoagulants (DOACs) should be withheld [20]. Four-factor prothrombin complex concentrate (PCC) should be considered in patients on warfarin with life-threatening lower GI bleeding and an INR >2.5 [21]. Fresh frozen plasma (FFP) can be given if PCC is not available [20,27]. Platelets should be transfused in patients with a low platelet count to maintain a platelet count of >30,000/microL in patients with severe lower GI bleeding and >50,000/microL in patients who require endoscopic management [21]. In patients with life-threatening lower GI bleeding on DOACs, reversal agents may be needed for the small subset of patients that do not respond to initial resuscitation and cessation of the anticoagulant. Targeted reversal agents (idarucizumab for dabigatran and andexanet alfa for apixaban and rivaroxaban) should be used if reversal is needed. Platelets should not be transfused in patients with normal platelet counts who are on antiplatelet medications [28]. Platelet and plasma transfusions should also be considered in patients who receive massive RBC transfusions (>3 units of packed RBCs within one hour). In patients with an INR of 1.5 to 2.5, endoscopic hemostasis may be performed before or concomitant with the administration of reversal agents. However, in patients with an INR >2.5, reversal agents should generally be administered before endoscopy. In all cases, the risk of reversing or holding anticoagulation should be weighed against the risk of continued bleeding without reversal. In some cases (eg, stopping aspirin in a patient who is taking it solely for primary prevention of cardiovascular disease), the decision to stop these agents may be straightforward. However, in more complicated cases, consultation with the provider who prescribed the medication may be needed. We recommend against the use of antifibrinolytic agents such as tranexamic acid in patients with acute lower GI bleeding [21].

In general, aspirin should be continued for secondary prophylaxis in patients with high-risk cardiovascular disease [20]. Dual antiplatelet therapy should not be discontinued without cardiology consultation in patients with an acute coronary syndrome within the past 90 days or with a bare-metal stent placed within the preceding six weeks or drug-eluting stents within the preceding six months [20,29]. In studies of patients with peptic ulcer bleeding and cardiovascular disease, discontinuation of aspirin is associated with increased all-cause mortality [30,31]. (See "Management of anticoagulants in patients undergoing endoscopic procedures", section on 'Urgent procedures' and "Gastrointestinal endoscopy in patients with disorders of hemostasis" and "Management of bleeding in patients receiving direct oral anticoagulants".)

When to resume these medications once hemostasis has been achieved will also depend on the patient's risks for thrombosis and recurrent bleeding. If low-dose aspirin or antiplatelet agents are withheld, they should be resumed, preferably within five days, or earlier if hemostasis has been achieved or there is no further evidence of bleeding [20]. (See "Management of anticoagulants in patients undergoing endoscopic procedures", section on 'Resuming anticoagulants after hemostasis'.)

DIAGNOSTIC STUDIES — Colonoscopy is the initial examination of choice for the diagnosis and treatment of acute lower GI bleeding (algorithm 1) [12]. Other diagnostic procedures that may be useful include radionuclide imaging, computed tomographic (CT) angiography (multidetector row helical CT), and mesenteric angiography (table 1). These radiographic procedures require active bleeding at the time of examination in order to identify a bleeding source and are therefore reserved for the subset of patients with severe, ongoing bleeding. Recommendations regarding the evaluation of patients with lower GI bleeding are based largely on clinical experience and the characteristics of the individual tests; no large randomized trials have demonstrated a clear advantage of a particular strategy. (See 'Consider an upper GI bleeding source' above.)

Colonoscopy — Colonoscopy is the diagnostic test of choice for hemodynamically stable patients with a lower GI bleed [21]. Advantages of colonoscopy compared with other tests for lower GI bleeding include its potential to precisely localize the site of the bleeding regardless of the etiology or rate of bleeding, the ability to collect pathologic specimens, and the potential for therapeutic intervention [7,9,32]. Disadvantages of colonoscopy include the need for bowel preparation, poor visualization in an unprepared or poorly prepared colon, and the risks of sedation in an acutely bleeding patient. Complications are reported in fewer than 2 percent of colonoscopies performed for lower GI bleeding [33]. Colonoscopy may not be needed in patients with previous presumptive or definitive diverticular bleeding who present with modest blood loss that stops spontaneously, and who have had a high-quality colonoscopy within 12 months with an adequate bowel preparation and no colorectal neoplasia [21].

The colonic mucosa should be carefully inspected during both insertion and withdrawal. Aggressive lavage may be needed to localize the bleeding site. The terminal ileum should be inspected to rule out bleeding from a proximal lesion in the small bowel. The use of a clear cap on the tip of the colonoscope can assist in detection and treatment of bleeding [21]. A definitive or potential bleeding source is visualized in 45 to 90 percent of patients undergoing colonoscopy for lower GI bleeding [34]. Visualization of a potential bleeding site that is not actively bleeding does not exclude the presence of a more proximal source. The identification of more than one potential bleeding site is common (eg, diverticulosis and hemorrhoids). Furthermore, a bleeding site is not always identified [35,36]. In the case of diverticular bleeding, blood and clots may be seen in numerous nonbleeding diverticula, making identification of the bleeding diverticulum difficult.

Endoscopic therapy can be used to treat many causes of lower GI bleeding, including diverticula, angiodysplasia, hemorrhoids, postpolypectomy bleeding, and radiation telangiectasia or proctitis [37-46]. The approach to treatment of these lesions is discussed in detail elsewhere. (See "Colonic diverticular bleeding" and "Angiodysplasia of the gastrointestinal tract", section on 'Endoscopic treatment' and "Management and prevention of bleeding after colonoscopy with polypectomy".)

Timing of colonoscopy — Colonoscopy should be performed on a next available basis during their hospitalization after adequate colon preparation in patients presenting with lower GI bleeding (algorithm 1) [20,21]. A randomized controlled trial of 159 patients with lower GI bleeding performed in 15 centers found no difference in identification of stigmata of recent hemorrhage, rebleeding, or blood transfusions in patients undergoing colonoscopy in less than 24 hours of presentation versus within 24 to 96 hours [47]. In addition, three smaller, single-center randomized trials found no difference in transfusion requirements, length of hospital stay, need for surgery, or mortality between urgent and delayed colonoscopy [10,48,49]. In one trial, urgent colonoscopy improved detection of the source of bleeding compared with expectant/elective colonoscopy alone or with radiographic interventions [48].

Bowel preparation — The colon should be cleaned of stool and blood prior to colonoscopy [21]. An unprepped evaluation should be reserved for lower GI bleeding when the source is highly suspected or known to be in the anorectal area or distal colon. We administer four to six liters of polyethylene glycol over three to four hours until the rectal effluent is clear [7,21,50]. However, split-dose preparation and/or the use of low-volume preparations may also be used [21,51,52]. In either case, additional preparation should be given if the preparation quality remains poor. However, studies of colonoscopy without preparation for lower GI bleeding generally report low cecal intubation rates, and blood or stool in the colon lumen can obscure the bleeding source [7,32]. (See "Bowel preparation before colonoscopy in adults".)

Caution should be used in patients at risk of aspiration or fluid overload. Some authors recommend metoclopramide (10 mg) at the start of the bowel preparation to facilitate intestinal transit and minimize the risk of nausea and vomiting, though this is not our practice [46]. During colonic lavage, the bleeding rate may appear to increase due to the rapid clearance of blood from the colon. However, there is no evidence that bowel preparation reactivates or increases the rate of bleeding. Radiographic studies should be obtained prior to colonic preparation if perforation or obstruction is suspected.

An experimental approach using water-jet pumps and mechanical suction devices ("hydroflush colonoscopy") has been described as an alternative to administering an oral lavage [53]. In a series of 12 patients with severe lower GI bleeding who underwent 13 hydroflush colonoscopy procedures, the examination was completed to the cecum in 9 of 13 procedures (69 percent), with adequate visualization for a definite or presumptive diagnosis reported in all 13. A definite source of bleeding was identified in five patients (39 percent). It is our opinion that this technique is best used as an adjunct to oral bowel preparation.

Radiographic imaging — An advantage of all radiographic tests for GI bleeding is the ability to diagnose bleeding throughout the GI tract, including small bowel sources. In addition, treatment of the bleeding site can be attempted during angiography (but not radionuclide imaging or CT angiography). However, these studies all require active bleeding at the time of the study in order to detect a bleeding site. In patients with severe bleeding who cannot be stabilized for colonoscopy or with severe ongoing bleeding despite colonoscopy, CT angiography may be used to select patients with active bleeding for subsequent angiography or, less commonly, to localize the source prior to surgery. It is important that angiography be performed promptly after a positive CT angiography [54]. Otherwise, the patient may stop bleeding by the time the angiography is completed, thereby missing the opportunity for embolization. (See "Angiographic control of nonvariceal gastrointestinal bleeding in adults".)

CT angiography — In patients with ongoing hemodynamically significant hematochezia, CT angiography is the initial diagnostic test of choice [21]. Patients with extravasation on a CT angiography should undergo prompt (ideally within 90 minutes) transcatheter arteriography and possible embolization (see 'Angiography' below). Multiple reports have described CT angiography for the localization of active hemorrhage [55-61]. CT angiography is an appealing diagnostic modality because it is widely available, fast, and minimally invasive. In addition, it provides anatomic detail that may be helpful for subsequent interventions such as angiography.

Bleeding at a rate of 0.3 to 0.5 mL/minute can be detected with CT angiography [62]. CT angiography is typically performed using multidetector row helical CT. Compared with single-detector row helical CT, multidetector row helical CT permits markedly increased resolution and shortens scanning time. This allows for improved identification of extravasated contrast material into the intestinal lumen.

Several studies have examined CT angiography for the detection of GI bleeding:

●A meta-analysis of 22 studies with 672 patients found that CT angiography had a sensitivity of 85 percent and a specificity of 92 percent for detecting active GI bleeding [63].

●In a review of 124 cases, the accuracy of CT angiography was 100 percent [33].

●In a study of 161 patients who underwent angiography, CT angiography was similar to radionuclide imaging for detecting bleeding on subsequent angiography (sensitivity of 90 percent, specificity of 20 percent), but it was more precise when it came to localizing the site of the bleeding [61].

However, CT angiography lacks therapeutic capability, requires radiation exposure, and utilizes intravenous contrast, which can be associated with nephropathy and allergic reactions [56]. Like the other radiographic tests for GI bleeding, a positive scan requires active bleeding. (See "Contrast-associated and contrast-induced acute kidney injury: Clinical features, diagnosis, and management".)

Angiography — Angiography requires active blood loss of 0.5 to 1.0 mL/minute under optimal conditions for a bleeding site to be visualized [64]. Angiography is typically reserved for patients in whom endoscopy is not feasible due to severe bleeding with hemodynamic instability [12,20].

CT angiography is commonly used to identify and localize the bleeding source prior to angiography [21,54]. Angiographies performed within 90 minutes of positive CT angiograms are more likely to detect bleeding than those that are delayed beyond this time frame. Some studies suggest that the frequency of negative arteriograms can be reduced by using radionuclide imaging to screen for active bleeding [65,66]. However, other studies have found no difference in the proportion of positive studies with or without preceding radionuclide imaging [67]. The incidence of negative tests is increased by the delay inherent in performing nuclear scans [68]. There are no randomized trials that compare the relative value of angiography guided by radionuclide imaging or CT angiography versus angiography alone, and results from case series are mixed [66,67].

In the absence of prior localization (eg, radionuclide imaging), the superior mesenteric artery is generally examined first in patients with presumed lower GI bleeding because bleeding sources tend to occur in bowel supplied by this artery (image 1) [69]. If this test is negative, the inferior mesenteric and celiac vessels are studied. The success rate varies widely from 25 to 70 percent, depending on the timing relative to the episode of bleeding and local expertise [7,68,70,71]. (See "Angiographic control of nonvariceal gastrointestinal bleeding in adults".)

The advantages of angiography over other tests for lower GI bleeding are that it does not require bowel preparation and anatomic localization is accurate. It also permits therapeutic intervention. (See "Angiographic control of nonvariceal gastrointestinal bleeding in adults", section on 'Intra-arterial vasopressin'.)

Transcatheter embolization is a means of controlling hemorrhage and has largely replaced other temporizing interventions such as vasopressin infusion. Superselective embolization of distal vessels using coaxial catheters decreases the risk of bowel infarction. A meta-analysis found that in patients with active bleeding, superselective embolization is feasible in 98 percent, and complications occur in 4.6 percent, most commonly bowel infarction or ulceration [72]. (See "Angiographic control of nonvariceal gastrointestinal bleeding in adults", section on 'Embolization'.)

Radionuclide imaging — We do not perform red blood cell scintigraphy in the setting of acute lower GI bleeding because of its limited accuracy in identifying the location of the bleeding site and logistical constraints [21]. Radionuclide scanning detects bleeding that is occurring at a rate of 0.1 to 0.5 mL/minute, and it is the most sensitive radiographic test for GI bleeding [73]. It is important that angiography be performed promptly after a positive radionuclide scan to localize the source of bleeding. However, a major disadvantage of radionuclide imaging is that it can only localize bleeding to a general area of the abdomen.

Accuracy rates have varied substantially across reports, ranging from 24 to 91 percent [74-77]. Poor localization occurs because blood can move in either a peristaltic or antiperistaltic direction. In addition, localization to an area of the abdomen is not equivalent to identifying a specific site. As an example, bleeding in a redundant sigmoid colon may appear as extravasated blood in the right lower quadrant, suggesting right colon bleeding. These difficulties were illustrated in a study of 203 patients undergoing technetium-99m (99mTc)-labeled red blood cell scintigraphy for lower GI bleeding [78]. The scan was positive and suggested a site of bleeding in 52 cases (26 percent). However, the scan was incorrect in 13 of these 52 patients (25 percent), and eight patients had unwarranted surgical procedures.

Additional testing if the bleeding site is not identified — A bleeding site may not be evident in some patients despite lower GI evaluation. If not already done, an upper endoscopy or push enteroscopy should be considered in those with severe, ongoing bleeding since up to 15 percent of such patients have a bleeding site in the upper digestive tract [10]. Push enteroscopy (endoscopy using a pediatric colonoscope or a dedicated enteroscope) allows visualization of approximately the proximal 60 cm of the jejunum [79].

Bleeding sites can also arise in more distal segments of the small bowel. There are several methods to evaluate the small intestine, such as capsule endoscopy and deep small bowel enteroscopy. (See "Evaluation of suspected small bowel bleeding (formerly obscure gastrointestinal bleeding)".)

In some patients, bleeding may have stopped, making efforts to identify the site more difficult. Such patients should be observed for 24 to 48 hours. An urgent CT angiogram/tagged red blood cell scan can be obtained to localize the region of bleeding if bleeding resumes. (See 'Radionuclide imaging' above.)

Provocative challenges with vasodilators, anticoagulants, and/or thrombolytics have been reported to aid in the diagnosis of elusive bleeding [80-82]. However, the risk of serious complications including refractory bleeding and death is substantial, and these methods should be used extremely rarely and only by expert centers after careful planning.

TREATMENT OF THE BLEEDING SITE — The treatment of lower gastrointestinal (GI) bleeding depends on the source of the bleeding. In many cases, the bleeding can be controlled with therapies applied at the time of colonoscopy or angiography. Rarely, patients with exsanguinating lower GI bleeding will need immediate surgery. The morbidity and mortality associated with colectomy in the absence of preoperative localization of a bleeding site are higher than in patients who have a bleeding site identified prior to surgery [83,84]. Thus, all efforts should be made to identify the bleeding source prior to surgery.

The treatment of lower GI bleeding is discussed in detail elsewhere. (See "Angiodysplasia of the gastrointestinal tract", section on 'Treatment' and "Colonic diverticular bleeding", section on 'Management' and "Management and prevention of bleeding after colonoscopy with polypectomy", section on 'Management' and "Argon plasma coagulation in the management of gastrointestinal hemorrhage" and "Angiographic control of nonvariceal gastrointestinal bleeding in adults", section on 'Angiographic therapies'.)

RECURRENT LOWER GI BLEEDING — In patients with significant, early (during the initial hospitalization) recurrent lower gastrointestinal bleeding, a repeat colonoscopy should be performed with endoscopic hemostasis if indicated [85]. Factors associated with rebleeding include the presence of underlying comorbidities, antiplatelet/anticoagulant/NSAID use, source of bleeding, and the initial modality of hemostasis [86,87].

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: Gastrointestinal bleeding 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 topics (see "Patient education: Colonoscopy (The Basics)" and "Patient education: Upper endoscopy (The Basics)" and "Patient education: Bloody stools in adults (The Basics)" and "Patient education: GI bleed (The Basics)")

●Beyond the Basics topics (see "Patient education: Colonoscopy (Beyond the Basics)" and "Patient education: Upper endoscopy (Beyond the Basics)" and "Patient education: Blood in the stool (rectal bleeding) in adults (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Clinical manifestations – Acute lower gastrointestinal (GI) bleeding refers to blood loss of recent onset originating in the colon. A patient with lower GI bleeding typically reports hematochezia (passage of maroon or bright red blood or blood clots per rectum). Blood originating from the left colon tends to be bright red in color, whereas bleeding from the right colon usually appears dark or maroon colored and may be mixed with stool. Rarely, bleeding from the right side of the colon will present with melena. (See 'Clinical manifestations' above.)

●Initial evaluation – The initial evaluation includes a history, physical examination, laboratory tests, and in some cases, upper endoscopy (algorithm 1). The goal of the evaluation is to assess the severity of the bleed, assess whether the bleeding may be coming from the upper GI tract, and determine if there are conditions present that may affect subsequent management. (See 'Initial evaluation' above.)

●Initial management – The initial management of a patient with suspected acute lower GI bleeding includes triage to the appropriate setting for management (outpatient, inpatient, intensive care unit), general supportive measures (eg, oxygen, establishment of adequate intravenous access), appropriate fluid and blood product resuscitation, and management of coagulopathies, anticoagulants, and antiplatelet agents. (See 'Initial management' above.)

●Diagnostic studies – Once an upper GI bleeding source is excluded, colonoscopy is the initial examination of choice for the diagnosis and treatment of acute lower GI bleeding (algorithm 1). Mesenteric angiography with or without preceding CT angiography, depending on institutional expertise, is appropriate in the small subset of patients with massive bleeding that cannot be stabilized for colonoscopy (table 1). (See 'Diagnostic studies' above.)

●Treatment of the bleeding source – The treatment of lower GI bleeding depends on the source of the bleeding. In many cases, the bleeding can be controlled with therapies applied at the time of colonoscopy or angiography. Rarely, patients with exsanguinating lower GI bleeding will need immediate surgery. The treatment of lower GI bleeding is discussed in detail elsewhere. (See "Angiodysplasia of the gastrointestinal tract", section on 'Treatment' and "Colonic diverticular bleeding", section on 'Management' and "Management and prevention of bleeding after colonoscopy with polypectomy", section on 'Management' and "Argon plasma coagulation in the management of gastrointestinal hemorrhage" and "Angiographic control of nonvariceal gastrointestinal bleeding in adults", section on 'Angiographic therapies'.)