Diagnostic role of pleural fluid adenosine deaminase in tuberculous pleural effusion

Between June 1998 and June 2000, 132 consecutive patients with symptomatic exudative lymphocytic pleural effusion were studied to evaluate the diagnostic role of pleural fluid adenosine deaminase (ADAPF) levels. The mean age was 52.2 (SD 16.3) years. The male to female ratio was 1.4:1. The analysis of ADAPF levels was measured base on Giusti's method. Tuberculous pleural effusion was diagnosed in 50 patients (37.9%). Another 59 patients (44.7%) had malignancies, 23 patients (17.4%) had miscellaneous other etiologies (including; 19 with chronic inflammations, 3 with melioidosis, and 1 with systemic lupus erythrematosus). The percentages of pleural fluid lymphocytes and pleural fluid protein in the tuberculous pleural effusion were similar to those with malignancies, but higher than those in the miscellaneous group. The mean value of ADAPF in the tuberculosis group was 93.2 (SD 56.5) U/l, which was significantly higher than for the malignancy and miscellaneous groups (p<0.05, one-way ANOVA). The mean values of ADAPF in the malignancy group were 36.7 (SD 39.2) U/l, and 31.3 (SD 23.4) U/l in miscellaneous group. Three patients were diagnosed with melioidosis and had ADAPF levels of 15, 46.9, and 49.8 U/l, respectively. One patient with systemic lupus erythrematosus had ADAPF levels of 24.1 U/l. A receiver operating characteristic (ROC) curve identified ADAPF level of 48 U/l as the best cut-off value, which in turn yielded a sensitivity of 80% (95% CI, 73 to 87%) and specificity of 80.5% (95% CI, 73.6 to 87.4%). The positive and negative predictive values at this cut-off value were 71.4% and 86.8%, respectively. The likelihood ratios for the diagnosis of tuberculous pleural effusion in patients with ADAPF levels less than 45 U/ l were 1:4, between 45 and 100 U/l were 5:2, and greater than 100 U/l were 7:1. We concluded that ADAPF levels are a useful diagnostic test for tuberculous pleural effusion. In addition, The analyis of ADA levels can be done simply, quickly, and cheaply.