[Cholesterol in pleural fluid. Its usefulness in differentiating between exudates and transudates].

To analyze the usefulness of cholesterol levels in the differentiation of exudates and transudates. A 3.5-year prospective study of 170 patients with pleural discharge. Clinical microbiological and cyto-histological criteria were used for diagnosis. Exudates were classified by Light's criteria, by cholesterol > or = 45 mg/dl in pleural liquid, by a cholesterol in pleural liquid/cholesterol in serum quotient > or = 0.3 and by a finding of both LDH and cholesterol in pleural fluid. These criteria were compared with the final etiological diagnosis. Only pleural discharges with confirmed etiological diagnoses were analyzed. In the 130 pleural discharges for which certain etiological diagnoses were obtained, 33 were transudates and 97 were exudates. Light's criteria allowed accurate classification of 92 (95%) of the 97 exudates and 30 (91%) of the 33 transudates. The cholesterol in pleural liquid/cholesterol in serum quotient was the most productive and useful parameter (96% sensitivity, 97% specificity), better than pleural fluid cholesterol and the Light's criteria. The association of LDH and pleural fluid cholesterol classified 100% of the exudates, with efficacy similar to that of Light's criteria. The cholesterol in pleural fluid/serum quotient was the most useful biochemical variable. Cholesterol levels were about as useful as Light's criteria. The association of LDH and cholesterol allows us to bypass blood analyses for the diagnosis of exudates.