Lysozyme (muramidase) in pleural effusions and serum

The authors evaluated the usefulness of paired pleural fluid and serum lysozyme determination in the differential diagnosis of pleurisies in 118 patients. Lysozyme activity of tuberculous effusions was found significantly higher (P less than 0.001) than that of effusions due to malignancy or heart failure, but considerable overlap of the individual values was observed. All patients with tuberculous pleurisy or tuberculous empyema, as well as a group of patients with suspected tuberculous effusion, had pleural fluid to serum lysozyme ratio of 1.0 or greater. In the remaining groups, only three patients, one with malignancy, one with lupus erythematosus, and one with sarcoidosis, exceeded this value. Their results suggest that pleural fluid to serum lysozyme ratio can be applied effectively in the differential diagnosis of tuberculous pleurisy.