Diagnostic efficacy of Adenosine deaminase activity in patients with very low CD4 counts and pulmonary tuberculosis

Adenosine deaminase activity (ADA) is a commonly used marker for the diagnosis of pulmonary tuberculosis (PTB). There have been concerns about its usefulness in immune-compromised pa-tients, especially HIV positive patients with very low CD4 counts. The objective of this study was to evaluate the sensitivity of ADA in HIV sero-positive patients having low CD4 counts, and compare it with its sensitivity in HIV sero-negative patients. Suspected tubercular patients on the basis of clinical and radiological grounds were subjected to laboratory diagnosis for confirmation of pulmonary tuberculosis and HIV status after an informed consent. Each patient was evaluated for serum adenosine deaminase activity (ADA) (by the sensitive colorimetric method described by Guisti), HIV (by Enzyme linked immune sorbent assay (ELISA) test), and CD4 counts. Out of a total 150 PTB patients, 120 were HIV sero-negative and 30 were HIV sero-positive. In HIV sero-positive PTB patients, the overall sensitivity, specificity, positive predictive value and negative predictive value of ADA was 93%, 95%, 96%, and and 90% respectively, as compared to 95%, 95%, 99% and 76% in HIV in sero-negative PTB. The mean ADA value was 87.1+36.24 in HIV patient with CD4 count >200 cell/microL (mean CD4 count245 cell/microL), as compared to 71.32+36.35 in patients with CD4 count 0.05). There was no correlation between ADA activity and CD4 count (r = -0.460, p< 0.05). We concluded that ADA analysis is a sensitive marker for diagnosis of pulmonary tuberculosis even in HIV patients with very low CD4 counts especially in a high TB endemic region, like India.