The nephrotic syndrome was diagno-»ed when the patient had proteinuria, edema, and hypoalbuminemia. Malignant effusions were confirmed by cytology, pleural biopsy, or autopsy. A diagnosis of pulmonary emlx)lus or infarction was made when there was a strong clinical suspicion and a high-probabilitv ventilation-perfusion scan or positive angiogram. Parapneumonic effusions were diagnosed when there was an associated infiltrate with signs of infection but with a negative Gram stain and culture of the pleural fluid. Postpericardiotomy syndrome was diagnosed when the patient was studied after coronary artery bypass or myocardial infarction and presented with appropriate symptoms and signs to include an associated pericardial effusion. Other clinical diagnoses of pleural effusions were accepted when the etiology could be categorized as an exudate or transudate.
After 27 patients were collected, the best discriminating level of the serum-effusion albumin gradient between transudates and exudates was established. This criterion was then applied to the next 32 patients prospectively.
The values obtained for each of Light s criteria and the albumin gradient were analyzed using the unpaired f-test to assess the significance of the separation between transudates and exudates. The sensitivity and specificity for Lights criteria and the albumin gradient were computed using Bayes’ theorem and were compared using McNemar s exact test for correlated proportions.