VALUE OF ADENOSINE-DEAMINASE IN THE DIAGNOSIS OF TUBERCULOUS PLEURAL EFFUSIONS IN YOUNG-PATIENTS IN A REGION OF HIGH PREVALENCE OF TUBERCULOSIS

Background - Pleural biopsy is usually considered important for the di agnosis of pleural effusions, especially for distinguishing between tu berculosis and neoplasia, even though tuberculous pleural fluid contai ns sensitive biochemical markers. In regions with a high prevalence of tuberculosis, and in patient groups with a low risk of other causes o f pleurisy, the positive predictive value of these markers is increase d. The criteria for performing a pleural biopsy under these circumstan ces have been investigated, using adenosine deaminase (ADA) as a pleur al fluid marker for tuberculosis. Methods - One hundred and twenty nin e patients with a pleural effusion aged less than or equal to 35 years (mean (SD) 25.2 (4.9) years) were studied. Seventy three were men. Ei ghty one effusions (62.8%) were tuberculous, 12 (9.3%) parapneumonic, and 10 (7.7%) neoplastic, five were caused by pulmonary thromboembolis m, four by systemic lupus erythematosus, seven by empyema, three follo wing surgery, one was the result of asbestosis, and one of nephrotic s yndrome. In five cases no definitive diagnosis was reached. ADA levels were determined by the method of Galanti and Giusti. Results - The di agnostic yield of procedures not involving biopsy was 94.5% (122/129). Pleural biopsy provided a diagnosis in a further two cases, but not i n the remaining five. All tuberculous cases had pleural fluid levels o f ADA of >47 U/1 (mean (SD) 111.1 (36.6) U/1). The only other cases in which ADA exceeded this level were six of the seven patients with emp yema. Cytological examination of the pleural fluid diagnosed eight of the 10 neoplastic cases, compared with six diagnosed by pleural biopsy . Conclusions - In a region with a high prevalence of tuberculosis pro cedures not involving pleural biopsy have a very high diagnostic yield in patients with a pleural effusion aged less than or equal to 35 yea rs, making biopsy necessary only in cases in which pleural levels of A DA are below 47 U/1, pleural fluid cytology is negative and, in the ab sence of a positive basis for some other diagnosis, neoplasia is suspe cted.