Measurement of pleural fluid cholesterol and lactate dehydrogenase. A simple and accurate set of indicators for separating exudates from transudates.

OBJECTIVES: To evaluate the usefulness of diverse combinations of pleural cholesterol concentration, pleural or serum protein, and lactate dehydrogenase (LDH) levels for the differentiation of pleural exudates and transudates.
DESIGN: Prospective laboratory study of pleural effusions.
SETTING: Medical school hospital. PATIENTS: One hundred eighty consecutive internal medicine ward patients in whom the etiologic diagnosis of their pleural effusion was confirmed. MEASUREMENTS: Cholesterol concentration in pleural fluid and protein and LDH both in pleural fluid and blood serum.
RESULTS: According to their etiology, 49 (27.2%) of the effusions were transudates and 131 (72.7%) were exudates. Using a cutoff point of 45 mg for pleural cholesterol and values for protein and LDH of Light et al, the best diagnostic power corresponded to the combination of pleural cholesterol and LDH: cholesterol level over 45 mg/dL and/or LDH over 200 IU/L identified exudates with a sensitivity of 99% and a specificity of 98%. All the other combinations showed inferior values and the criteria of Light et al reached 98 and 82%, respectively.
CONCLUSIONS: The measurement of pleural cholesterol and LDH permits the separation of pleural exudates from transudates with an accuracy similar to the original report of Light et al, with the advantage of requiring only two laboratory determinations and no simultaneous blood sample.