Pleural fluid characteristics of common conditions

Suspected condition	Pleural fluid analysis	Diagnostic or other features
Uncomplicated parapneumonic effusion	Serosanguinous, nonpurulent exudate Glucose variable but usually >60 mg/dL pH usually normal to low (7.2 to 7.4; very low pH is unusual but usually >7.2) Elevated WBC (PMNs)	Fluid nonloculated on imaging studies.
Complicated parapneumonic effusion/empyema	Serosanguinous or purulent exudate Glucose often <40 mg/L (2.2 mmol/L) LDH usually markedly elevated (sometimes >1000 units/L) Normal to low pH (<7.15 supports need for pleural fluid drainage, empyema often has pH <7) Elevated WBCs (PMNs)	Identification of microorganism on pleural fluid staining or culture. Frank pus is diagnostic of an empyema. Fluid loculated on imaging studies.
Malignancy	Serous, serosanguinous, or sanguinous exudate; 10% may be transudative by Light's criteria Low glucose (may be <40 mg/L [2.2 mmol/L] in some cases) Low pH (<7.4; may be <7.2 in some cases) Elevated WBC (PMNs; lymphocytes [if longstanding]) Basophils >10% suggests leukemic involvement of the pleura	Identification of malignant cells on cytology or cell block is diagnostic (may need repeat sampling). Other features, including elevated amylase and ADA, are nonspecific. High clinical suspicion with negative initial cytology warrants repeat thoracentesis for cytology or rapid progression to pleural biopsy.
CHF	Serous or serosanguinous transudate Normal glucose pH 7.4 to 7.55 May contain WBC and RBC if associated bleeding Elevated serum and pleural fluid NT-proBNP	Classic features of pulmonary edema on chest radiography. Serum NT-proBNP usually suffices to support diagnosis of CHF, obviating need for pleural fluid NT-proBNP.
Tuberculosis	Serous or serosanguinous exudate Low glucose (60 to 100 mg/dL [3.3 to 5.6 mmol/L] in many; <50 mg/dL [2.8 mmol/L] in 20%; <30 mg/dL [1.7 mmol/L] in <10%) Low pH (<7.4; pH <7.30 in approximately 20% of cases) Elevated WBC (lymphocytes; occasionally PMNs in early disease) ADA >40 units/L Mesothelial cells >10% (in rare cases)	Identification of microorganism on microbiologic stain or culture is diagnostic.
Pancreatitis	Serous or serosanguinous exudate Normal glucose pH 7.4 to 7.55 Pancreatic amylase 1000 IU/L Pleural fluid-to-serum amylase ratio >2 Elevated WBC (PMNs) and RBC if associated bleeding	Imaging and biochemical findings support the diagnosis of pancreatitis.
Ruptured esophagus	Serous or serosanguinous exudate Low glucose (often <40 mg/L [2.2 mmol/L]) Low pH (often <7.2) Elevated salivary amylase Food particles in pleural fluid Elevated WBC (typically PMNs)	Contrast imaging is typically required to demonstrate the ruptured viscus.
Chylothorax	Milky fluid (especially after a high-fat diet but may be serous or sanguinous) Exudative but sometimes transudative Normal glucose Low LDH Normal pH but may be low in patients with malignant chylous effusions Triglyceride ≥110 mg/dL (≥1.24 mmol/L) Lymphocyte predominance (>70%)	A combination of lymphocytic effusion with pleural fluid triglyceride ≥110 mg/dL (1.24 mmol/L) in a patient with a known risk factor (eg, mediastinal trauma) is considered diagnostic. Lipoprotein analysis for chylomicrons may be needed in cases of uncertainty.
Cholesterol effusion*	Milky fluid or turbid/cloudy (may rarely be serous or serosanguinous) Exudate Normal glucose Low to normal pH Lymphocyte predominance Cholesterol level usually >200 mg/dL (5.17 mmol/L) Cholesterol-to-triglyceride ratio >1	A combination of cholesterol ≥200 mg/dL (≥5.18 mmol/L), triglyceride <110 mg/dL (1.24 mmol/L), and a cholesterol-to-triglyceride ratio >1 in a patient with a known risk factor is typically sufficient to make the diagnosis. Rarely, the demonstration of cholesterol crystals under polarized light may be needed and is definitively diagnostic (absent in 10%).
Rheumatoid pleurisy	Local immunologic serositis: serous exudate Glucose may be <50 mg/dL Elevated LDH pH may be <7.2 WBC elevated (PMNs if acute, mononuclear if chronic) RF elevated Complement decreased Rupture of necrotic subpleural rheumatoid nodules into pleural space: sterile empyema with yellow-green exudate, low pH, low glucose, elevated LDH Rheumatoid vasculitis of pleura: bloody effusion Chylothorax and cholesterol effusions may occur in RA	In pleural effusion due to serositis, cytology may show multinucleated giant cells (tadpole cells).
SLE pleuritis	Usually small, bilateral serous or serosanguinous exudates Low glucose and pH in 20% Elevated WBC (PMNs; lymphocytes [if longstanding]) Decreased complement ANA titer ≥1:160	ANA titer ≥1:160 is a sensitive tool for distinguishing lupus pleuritis from other effusions in patients with SLE. LE cell preparation and a pleural fluid-to-serum ANA ratio ≥1 are nonspecific.
Hemothorax	Bloody Exudative Normal glucose (similar to that of serum concentration) Normal to slightly low pH Elevated RBC, pleural fluid-to-blood hematocrit ratio >0.5	A pleural fluid-to-blood hematocrit ratio >0.5 is considered diagnostic of hemothorax.

WBC: white blood cells; PMNs: polymorphonuclear neutrophils; LDH: lactate dehydrogenase; ADA: adenosine deaminase; CHF: congestive heart failure; RBC: red blood cells; NT-proBNP: N-terminal pro-brain natriuretic peptide; IU: international units; RF: rheumatoid factor; RA: rheumatoid arthritis; SLE: systemic lupus erythematosus; ANA: antinuclear antibody; LE: lupus erythematosus.

* Features typical of rheumatoid or tuberculous pleurisy or of parasitic infection may complicate the picture.

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Pleural fluid characteristics of common conditions