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Is ELISA a reliable test to diagnose tuberculosis?

Answered by: Dr Sanjay Bhattacharya

Associate Consultant, Department of Microbiology, Tata Medical Center, Kolkata

Q. I am a 26 years old male and my ELISA test results are as follows: IgA - 1311.14; IgG - 196.82; IgM - 0.21. I underwent anti-tuberculosis treatment 10 years back. How do I know whether the ELISA test results are showing a new infection or a relapse of past one? Is Mantoux a reliable test to diagnose TB?

A.  Serological tests such as ELISA (IgG, IgM or IgA) have very little value in the diagnosis of tuberculosis. In a systematic review it was found that the Anda-IgG enzyme-linked immunosorbent assay shows limited sensitivity (range 63% to 85%) and inconsistent specificity (range 73% to 100%) for the diagnosis of pulmonary TB. There was also wide variation noted in test performance depending on the kit used. There was insufficient data to determine the accuracy of most commercial tests in smear microscopy-negative patients, as well as their performance in children or persons with HIV infection. For extra-pulmonary TB the Anda-TB IgG kit showed highly variable sensitivity (range 0.26-1.00) and specificity (range 0.59-1.00) for all extra-pulmonary sites combined.

A.  Serological tests such as ELISA (IgG, IgM or IgA) have very little value in the diagnosis of tuberculosis. In a systematic review it was found that the Anda-IgG enzyme-linked immunosorbent assay shows limited sensitivity (range 63% to 85%) and inconsistent specificity (range 73% to 100%) for the diagnosis of pulmonary TB. There was also wide variation noted in test performance depending on the kit used. There was insufficient data to determine the accuracy of most commercial tests in smear microscopy-negative patients, as well as their performance in children or persons with HIV infection. For extra-pulmonary TB the Anda-TB IgG kit showed highly variable sensitivity (range 0.26-1.00) and specificity (range 0.59-1.00) for all extra-pulmonary sites combined.

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