Plasma levels of B-type natriuretic peptide (BNP) are increased in heart failure. The aim of this study was to assess the usefulness of BNP measurements in pleural fluid from patients with and without heart failure. The pro-BNP concentration was measured in 117 pleural fluid samples taken from patients with heart failure, malignant effusions, tuberculous pleurisy, parapneumonic effusions, hepatic hydrothorax, and effusions secondary to pulmonary embolism. In patients with heart failure the median level of pro-BNP was significantly higher than in all other groups (p<0.001). A pleural fluid BNP concentration of ⩾1500 pg/ml had a sensitivity of 91% and specificity of 93% for the diagnosis of cardiac failure and, furthermore, a high pro-BNP level helped to correctly identify those heart failure patients, mostly on diuretics, who were classed as having exudates according to Light’s criteria.

There are, however, limitations to the study. It is not reported whether pro-BNP levels were more predictive of heart failure than clinical variables such as a history of myocardial infarction, and it did not compare the pleural pro-BNP concentration with plasma BNP levels. Further studies are required to clarify the clinical usefulness of pleural fluid BNP assay.