Eighty-four patients (25 tb, 30 lung cancer and 29 COPD) were included in the study. ADA activity in sputum and serum was measured. Sputum ADA activities of tb patients were significantly higher than the other two groups (P < 0.05). Sputum/serum ADA ratios were similar in all groups. Sputum ADA activities between 150 and 200 U/L were the measurements with the best test performance according to the ROC curve. Sensitivity, specificity, positive predictive value, and negative predictive value were 44.0, 86.4, 57.8, 78.4% for 150 U/L and 32.0, 96.6, 80.0, 77.0% for 200 U/L, respectively. Area under the curve was 0.663. Because of low sensitivity, routine determination of ADA activity in sputum for the diagnosis of pulmonary tb is not recommended. However, it can be helpful in the diagnosis of smear-negative cases who are strongly suspected of tb.

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