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(1) 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(2) 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(1) in TB patients (P = 0.001). Sputum ADA and ADA(2) were higher in both AFB-positive and AFB-negative TB patients. Using a cut-off level of respectively 16 UI/l and 5UI/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.