Q: I am a 23 years old student weighing 55 kg. What is Mantoux test? What does ELISA IgG positive mean? Am I suffering from TB? I was injected by BCG in childhood.

A:Both Mantoux test and IgG ELISA measures previous exposure to the bacteria Mycobacterium tuberculosis. Mantoux test measures the cell mediated immune response to TB, whereas TB IgG ELISA measures antibody mediated immune response. Mantoux test or other similar tests for cell mediated immunity is the standard approach to detect previous exposure to tuberculosis. This is because TB is an intracellular pathogen. The value of antibody tests such as those done by ELISA although done is some settings, is not clear. The sensitivity and specificity of these the commercial tests (for serological diagnosis of TB) are highly variable. It is possible that after BCG vaccination, to give positive results with these tests.