Performance of Adenosine Deaminase assay in diagnosis of pulmonary & extrapulmonary tuberculosis

Adenosine Deaminase (ADA) estimation in all forms of tuberculosis (TB) is done by several investigators, however, there has been a lot of debate about the use of the ADA for TB diagnosis. In the present study, to overcome this debate, we have planned a large scale study in the Central India population for all forms of TB i.e. pulmonary TB (PTB), tuberculous meningitis (TBM), TB arthritis (TBAR), and abdominal tuberculosis (ATB) to access the performance of ADA for diagnosis of TB. In addition to that, we have also studied the performance of the ADA test in the prognosis of TB. ADA activity was evaluated using the method of Guisti and Galanti. To evaluate the role of the ADA test as a prognostic marker in TB, we have collected follow-up clinical samples of PTB and TBM cases. The sensitivity of the ADA test is impressive in all forms of TB clinical samples analyzed for the study (PTB [82%], TBM [85%] TBAR [85%]), and (ATB) [84%]. However, the specificity was variable as ADA test results were found to be satisfactory for extrapulmonary TB (EPTB) cases ( i.e TBM [89%], (ATB) [88%], TBAR [88%]), on the other hand, poor specificity was observed in PTB cases (PTB [48%]). In the follow-up clinical samples (collected before and after anti-TB treatment [ATT]). In the follow-up samples, the result of the ADA test was observed to have declined drastically thereby showing a negative value after the ATT. Our study, which consists of a large number of samples, suggests that the ADA has very limited value in the diagnosis of PTB, and hence it is not recommended for PTB diagnosis. On the other hand, the ADA test is found to be useful for the diagnosis of EPTB in correlation to the patient's clinical condition. Along with the above-mentioned aspects and according to our follow-up study results, we recommend that ADA be useful as a prognostic indicator for TB.