Q: Does a positive TB IgM Elisa test suggest that one might be HIV infected? I read that Elisa test is done for HIV as well.

A:Enzyme linked immuno-sorbent assay (ELISA) or Enzyme Immuno-assay (EIA) is an immunological diagnostic technique used to look for antigens (Ag) or antibodies (Ab) in a sample. It is used to test for HIV Ab (and Ag), Hepatitis B Ag and Ab, Abs to Hepatitis A, C and E, Abs to Entamoeba histolytica, etc. It is useful in the diagnosis of Hydatid disease, Dengue, ToRCH infections, cysticercosis, etc. Each ELISA is distinct using a specific kit meant for diagnosing a presence or absence of an antigen or antibody in a sample. IgM ELISA for TB looks for IgM antibodies against Mycobacterium tuberculosis in a sample. It has little diagnostic value since it has low sensitivity and specificity, since TB is endemic in most countries, and most people have been exposed to it. A positive result implies that the patient has most likely been exposed to TB bacilli in the recent past. The mere presence of IgM antibodies is not diagnostic of TB. HIV ELISA looks for antibodies against HIV, and is unrelated to IgM ELISA for TB. However, there could be co-infection of TB and HIV, so it would be prudent to check with your doctor why the test was done.