[Reappraisal of the standard method (Light's criteria) for identifying pleural exudates]

BACKGROUND AND OBJECTIVES: Light's criteria remain the best method for separating pleural exudates from transudates. We assessed their operating characteristics, as well as those resulting from omitting the pleural fluid to serum lactate dehydrogenase (LDH) ratio from the original criteria (abbreviated Light criteria), in a large series of patients. We also searched for the best combination of pleural fluid parameters, including protein, LDH and cholesterol that identify exudates.

PATIENTS AND METHOD: We conducted a retrospective study of 1,490 consecutive patients with pleural effusion who underwent a diagnostic thoracentesis. There were 1,192 exudates and 298 transudates. Sensitivity, specificity, area under ROC curve, and odds ratio for both individual and combined pleural fluid parameters were calculated.

RESULTS: Light's criteria yielded 97.5% sensitivity and 80% specificity. Both abbreviated Light criteria (sensitivity: 95.4%; specificity: 83.3%) and the combined use in an "or" rule of pleural fluid protein and LDH (sensitivity: 95.4%; specificity: 80,2%) had similar discriminative properties than standard criteria.

CONCLUSIONS: Diagnostic separation of pleural effusions into exudates or transudates can be done effectively thorough the abbreviated Light criteria when the serum LDH value is not available. On the other hand, if venipuncture wants to be avoided (an unusual circumstance) the combination of pleural fluid protein and LDH represents an alternative to Light's criteria.