Objectives: Pleural effusions due to congestive heart failure (CHF) typically are transudates, but an occasional patient with CHF is found to have an exudate in the absence of an apparent cause other than CHF. We sought to determine the incidence and clinical significance of such exudative effusions.

Design: Patients with CHF and effusions seen during the 7-year period from January 1994 through December 2000 were identified from their hospital discharge diagnoses and radiographs, while those who had undergone thoracentesis were identified from a review of the laboratory logs. The presenting symptoms and clinical course were determined from a review of the medical records. The effect of RBC contamination on pleural fluid lactate dehydrogenase (LDH) levels was determined by measuring the LDH activity of mock pleural fluid containing known amounts of RBC.

Results: Seven hundred seventy patients had CHF with an effusion, but only 175 patients underwent a thoracentesis. In this select group, 86 patients had transudates and 89 had exudates. A noncardiac cause for the exudate was readily identified in 59 patients by hospital discharge, and 7 more patients had an etiology found during follow-up. Eleven of the remaining 23 patients had undergone coronary artery bypass graft (CABG) surgery > or = 1 year prior to presentation, and 50% of the effusions in patients who had undergone CABG surgery were exudates. Thus, CHF-related exudates were identified in only 12 patients, and in 4 of these patients the exudates could be explained by RBC contamination of the pleural fluid. The clinical presentation of patients with CHF-associated exudates was similar to that of CHF patients with transudates.

Conclusion: In most patients who have CHF and an exudative effusion, there is a noncardiac cause for the pleural effusion. The high frequency of exudates in patients with a history of CABG indicates a persistent impairment in lymphatic clearance from the pleural cavity. Exudative effusions due solely to CHF are rare.