Diagnostic significance of pleural fluid lactate concentration in pleural and pulmonary diseases.

Pleural fluid samples from 198 patients were analysed in order to evaluate the usefulness of lactate concentration as a diagnostic test for separating infectious from non-infectious processes in the pleural cavity. Pleural fluid lactate was quantified by means of a gas chromatographic method. The highest lactate levels were found in patients with septic pleuritis. Significantly lower values were observed in cases with malignancies. With a cut off value of 10 mmol/l, the predictive value of a positive test was 0.94 and of a negative test 1.0. Because of the high predictive values of the test, measurement of lactate concentration in pleural fluid offers a rapid and useful information in the differentiation between infectious and non-infectious pleural disease.