Q: I am a 29 years old male who underwent medical checkup, which showed all reports as normal. But TB IgM came positive. Am I suffering from tuberculosis? There were no symptoms like cough, cold, fever and weight loss.

A:Serological tests such as TB IgM are generally not reliable in the diagnosis of tuberculosis. Although IgM reactivity is indicative of a new infection, however for TB the gold standard for diagnosis is isolation and identification of the organism (Mycobacterium tuberculosis) by culture, microscopy and other identification tests. In the absence of symptoms or signs which are indicative of TB (such as cough, fever and weight loss) the specificity (that is the ability to distinguish patients without disease from those with disease) is extremely limited. IgM serology moreover is associated with non-specific cross reactivity, where the tests falsely give positive results due to serological reactivity with other antigens which may be similar structurally. It is very likely that in your case the TB IgM reactivity is of no significance. When a doctor diagnoses a disease he/she looks at a number of factors. The positive result of one or more test may indicate some things in a particular direction but does not necessarily clinch the diagnosis.