Adenosine deaminase activity and its isoenzymes in the sputum of patients with pulmonary tuberculosis

BACKGROUND: Adenosine deaminase (ADA) has been widely used for the diagnosis of tuberculous pleural effusion. Two isoenzymes have been described, ADA(1) and ADA(2). OBJECTIVE: To evaluate the diagnostic value of sputum ADA, ADA, and ADA(2) activity in pulmonary tuberculosis (TB). DESIGN: We measured total ADA, ADA(1) and ADA(2) activity in the sputum of 27 patients with pulmonary TB (11 had a negative Ziehl-Neelsen stain for acid-fast bacilli [AFB]). Nineteen patients with lung cancer were used as controls. RESULTS: Sputum total ADA activity was significantly higher in TB than in lung cancer patients (median 18 U/l [range 3-70] vs. 6 U/l [2-16]; P < 0.001). Sputum ADA, activity was significantly higher in TB compared to lung cancer patients (9 U/l [0-65] vs. 5 U/l [0-12]; P = 0.001). Sputum ADA(2) was significantly higher than ADA, in TB patients (P = 0.001). Sputum ADA and ADA2 were higher in both AFB-positive and AFB-negative TB patients. Using a cut-off level of respectively 16 UI/l and 5 UI/l for sputum total ADA and ADA(2), sensitivity and specificity were 55.6% and 100% for total ADA and 81.5% and 63.2% for ADA(2). CONCLUSION: Sputum total ADA and ADA(2) levels are elevated in patients with pulmonary TB. As they are elevated even in AFB-negative patients, they may assist In the early diagnosis of pulmonary TB.