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How is tuberculosis diagnosed in asymptomatic patients?

Q: Q. What is the relevance of raised IgG - 366 (positive) and negative IgM to Mycobacterium tuberculosis in an asymptomatic person?

A:The diagnosis of TB cannot be made on the basis of serological assays in asymptomatic patients. At most, they can supplement the investigations in highly suspect cases, especially in diagnosing extra-pulmonary TB, and then also, all 3 antibody markers - IgG, IgM and IgA should be done for serological evaluation of TB. Since TB is endemic in India, most of us have been exposed to TB bacilli at some time in our childhood and consequently would have some titre of IgG antibodies against TB bacilli. IgM antibodies, in high titre, usually develop in cases with a history of recent exposure to TB bacilli. Based on the results of your TB ELISA reports, no conclusion can be drawn, since ELISA is a poor diagnostic modality for diagnosis of TB, having a low sensitivity and specificity, which means that it may miss many patients of TB, while wrongly diagnosing TB in others.


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