Comparative analysis of Light's criteria and other biochemical parameters for distinguishing transudates from exudates.

OBJECTIVES

To compare the accuracy of Light's criteria for categorizing a pleural effusion as an exudate with several alternative criteria.

DESIGN

Prospective evaluation of patients who underwent a diagnostic thoracocentesis.

SETTING

Community teaching hospital in Lleida, Spain.

PATIENTS AND METHODS

Medical records and pleural fluid characteristics of 241 consecutive patients with pleural effusion admitted over a 29-month period were reviewed. Forty eight of these patients were excluded for different reasons. Light's criteria and a different cutoff level for the pleural fluid cholesterol level were applied and their accuracies were calculated.

RESULTS

Of the 193 patients included, 38 (20%) had transudates and 155 (80%) exudates. The accuracy of Light's criteria for identifying exudates was 92% [confidence intervals (CI), 88-96%], with a sensitivity of 97% (CI, 94-100%) and specificity of 71% (CI, 57-85%). A cutoff level of 50 mg dl-1 was selected for pleural cholesterol, which yielded a sensitivity and specificity of 84% (CI, 79-90%), with an accuracy of 84% (CI, 72-96%). Overall, pleural cholesterol misclassified more exudates as transudates than Light's criteria (15 vs. 3.2%, P < 0.001). The combination of pleural cholesterol with lactate dehydroegnase (LDH) or pleural fluid/serum protein ratio revealed a comparable accuracy to that achieved with Light's criteria.

CONCLUSIONS

Light's criteria are just as useful as the association of pleural cholesterol and LDH to detect exudates. In the present study, no parameter, including pleural cholesterol, was superior to Light's criteria.