Background Light's criteria remain the standard for distinguishing exudative from transudative pleural effusions, but require serum sampling and lack specificity. We assessed whether a pleural fluid-only approach could match the diagnostic accuracy. Methods We analysed 7280 diagnostic thoracenteses from a single centre, divided into derivation (n=5000) and validation (n=2280) cohorts. We compared Light's criteria with a triple (protein >3 g·dL −1 , lactate dehydrogenase (LDH) >250 IU·L −1 or cholesterol >55 mg·dL −1 ) and a double (LDH >250 IU·L −1 or cholesterol >55 mg·dL −1 ) combination using sensitivity, specificity, likelihood ratios and area under the curve (AUC). AUCs were assessed using the DeLong method with multiple imputations from a mixed model. McNemar's test examined discordant classifications. Results The triple combination showed no significant AUC difference versus Light's criteria in either cohort and had equivalent sensitivity (99% versus 98% in derivation; both 98% in validation). In the derivation cohort, McNemar's test showed a small but statistically significant excess of false negative exudates with the triple combination (p<0.001), whereas no significant difference was found in the validation cohort (p=0.241). The triple combination correctly reclassified 19–20% of transudates misclassified by Light's criteria, while the reverse occurred in 11–14%. The double combination yielded the highest AUCs but missed more exudates, limiting its clinical safety. Conclusion A pleural fluid-only triple combination matches Light's criteria in diagnostic accuracy, avoids serum sampling and improves specificity with minimal sensitivity loss in one cohort. This approach may be a practical alternative for the initial classification of pleural effusion when blood sampling is unavailable or undesirable.
Porcel et al. (Sun,) studied this question.