Diagnostic significance of pleural fluid lactate concentrations.

Lactate concentrations in the pleural fluid and plasma of 57 patients with pleural effusions were measured by an enzymatic method. The mean pleural fluid lactate concentrations were significantly higher in patients with empyemas and rheumatoid arthritis than in patients with tuberculosis, cancer, non-specific pleural effusions and congestive heart failure. Pleural fluid lactate concentrations correlated significantly with pleural fluid lactate dehydrogenase activities and inversely with pleural fluid glucose concentrations. An elevated pleural fluid lactate concentration is not diagnostic for empyema, as most patients with rheumatoid arthritis and some with tuberculosis and cancer also show high values.