Background: Pleural effusion is not a pathognomonic sign and distinguishing between transudates and exudates often presents a diagnostic dilemma.
Objective: To examine whether the NT pro-brain natriuretic peptide (NT-proBNP) in pleural fluid is a diagnostic tool for determining the cardiac etiology of pleural effusions.
Methods: We measured pleural fluid and serum NT-proBNP levels in a consecutive series of 98 patients with heart failure and in 142 patients with other causes.
Results: The median pleural fluid NT-proBNP levels among the heart failure patients were significantly higher (3,310 pg/mL) than hepatic hydrothorax (16 patients, 531 pg/mL), malignant pleural effusion (38 patients, 733 pg/mL), parapneumonic pleural effusion (40 patients, 294 pg/mL), and tuberculous pleural effusion (64 patients, 214 pg/mL) (p<0.001). At a cut-off point of > or = 1,714 pg/mL, the test had a sensitivity of 99%, a specificity of 99 % for the diagnosis of heart failure. There were 28 patients with pleural effusion due to heart failure misclassified as exudates by Light's criteria. Ten cases of misclassified heart failure (36% of 28 patients) showed serum-effusion protein gradient less than 3.1 g/dL; 26 of them exhibited pleural fluid NT-proBNP levels of > or = 1,714 pg/mL. The 26 patients of misclassified heart failure received diuretics before thoracentesis. Pleural fluid NT-proBNP levels were correlated with serum NT-proBNP levels (R(2)=0.928, p<0.001).
Conclusion: Pleural fluid NT-proBNP may be useful in the diagnosis of pleural effusion resulting from heart failure. The test may be especially useful in heart failure patients with exudates who have been treated with diuretics.