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Background -Pleural biopsy is usually considered important for the diagnosis of pleural effusions, especially for distinguishing between tuberculosis and neoplasia, even though tuberculous pleural fluid contains sensitive biochemical markers. In regions with a high prevalence of tuberculosis, and in patient groups with a low risk of other causes of pleurisy, the positive predictive value of these markers is increased. The criteria for performing a pleural biopsy under these circumstances have been investigated, using adenosine deaminase (ADA) as a pleural fluid marker for tuberculosis. Methods -One hundred and twenty nine patients with a pleural effusion aged .35 years (mean (SD) 25 2 (4.9) years) were studied. Seventy three were men. Eighty one effusions (62.8%) were tuberculous, 12 (9.3%) parapneumonic, and 10 (7.7%) neoplastic, five were caused by pulmonary thromboembolism, four by systemic lupus erythematosus, seven by empyema, three following surgery, one was the result of asbestosis, and one ofnephrotic syndrome. In five cases no definitive diagnosis was reached. ADA levels were determined by the method of Galanti and Giusti.

In these patients, lymphocyte-rich exudative pleural effusions occurred, on average, at a young age, with no preference for either the right or the left side; normally affected no more than two thirds of the hemithorax; and were generally unaccompanied by pulmonary infiltrates. High ADA concentration was a highly sensitive diagnostic sign and was caused by a rise in ADA2 concentration. The most sensitive criterion based on pleural biopsy was the observation of caseous granulomas, and culture of biopsy material further increased overall sensitivity. Negative skin test results were no guarantee of the effusion being nontuberculous. This, together with the low mean age of the patients and the low frequency of associated pulmonary lesions, suggests that tuberculous pleural effusion is a primary form of tuberculosis in this region.

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