The diagnosis of an exudate is most accurate if cholesterol in the pleural fluid is greater than 55 mg/dL (LR range, 7.1-250), lactate dehydrogenase (LDH) is greater than 200 U/L (LR, 18; 95% CI, 6.8-46), or the ratio of pleural fluid cholesterol to serum cholesterol is greater than 0.3 (LR, 14; 95% CI, 5.5-38). A diagnosis of exudate is less likely when all Light’s criteria (a ratio of pleural fluid protein to serum protein >0.5, a ratio of pleural fluid LDH to serum LDH >0.6, or pleural fluid LDH >two-thirds the upper limit of normal for serum LDH) are absent (LR, 0.04; 95% CI, 0.02-0.11).
