Adenosine Deaminase (ADA), Ascitic Fluid

ADA is adenosine deaminase. ADA test is not a diagnostic test. ADA test along with other tests such as AFB smear, culture, fluid analysis, molecular testing with NAAT etc, helps to determine if there is tuberculous infection. ADA is an enzyme involved in purine metabolism and it is essential for the proliferation and differentiation of T-lymphoid cells. Hence ADA is considered as an index for cellular immunity. ADA has a role in the diagnosis of tuberculosis and is increased during the infection. ADA test is a rapid test and detects the bacteria (mycobacterium tuberculosis) even when they are present in a very few number. However ADA test is not specific for tuberculosis and the ADA levels are increased (usually not more than 100 IU/L) in other conditions such as non-tuberculous pleural effusion, malignancy (broncogenic carcinoma, mesothelioma etc), lymphoproliferative disorders, empyema and collagen vascular diseases like rheumatoid arthritis and systemic erythematosus etc. Hence though ADA test is more sensitive, it has less specificity. Culture for detection of tuberculosis is considered gold standard but the process takes a long duration of two to three weeks. Similarly the molecule test for TB, though sensitive, requires sufficient number of bacilli in the sample processed. AFB smear and the molecular tests are rapid detection methods. Though the ADA test is not a definitive test, this test along with other test like AFB smear and molecular test help in the management of treatment in suspecting cases of tuberculosis, till the culture results are obtained.

1. When is ADA test ordered?

ADA test is ordered mostly when there is accumulation of fluid (pleural, peritoneal etc) and symptoms suggestive of Tuberculosis such as cough, fever, weight loss etc.

2. Is it advised to get the ADA test done in all the suspected cases of tuberculosis?

The ADA test is not done as a routine test in all suspected cases of tuberculosis. the ADA test along with other tests such as AFB smear, helps in the treatment management, till the results of culture (gold standard method) are available.

3. On what all samples ADA test can be performed?

Most commonly ADA test is performed on pleural fluid, however ADA estimation can be done on ascitic fluid, pericardial fluid, CSF, synovial fluid etc.