Differential diagnosis of pleural effusion by lactate dehydrogenase isoenzyme analysis.

STUDY OBJECTIVE: To determine the diagnostic value of pleural fluid lactate dehydrogenase (LDH) isoenzyme analysis in the differential diagnosis of pleural fluid. PATIENTS AND METHODS: Eighty-seven consecutive patients with pleural effusion caused by congestive heart failure (33), infection (33), and malignancy (21) comprised a derivation set of patients. Pleural fluid LDH activity and isoenzyme pattern were established in all patients and analyzed by the classification and regression trees (CART) method. An additional group of 20 consecutive patients comprised a validation set that was used for cross-validation of CART-derived decision tree. RESULTS: A decision tree, with a positive predictive value of 83%, was constructed and validated by data from a validation set of patients. CONCLUSIONS: Pleural fluid LDH isoenzyme pattern may be helpful for the differential diagnosis of the most common causes of pleural effusions: congestive heart failure, infections, and malignancy.