IGRAS (Gamma Interfection) TB Gold in Dehradun

What is a IGRAS (Gamma Interfection) TB Gold?

An Interferon Gamma Release Assay is a blood test for tuberculosis infection. Your blood is exposed to proteins specific to Mycobacterium tuberculosis, and if your immune cells have met that organism before they release interferon gamma, which the test measures. Its critical advantage over the older Mantoux skin test is specificity: the proteins used are absent from the BCG vaccine, so prior BCG, which almost everyone in India has received, does not cause a false positive. It also needs only one visit, with no return trip 48 to 72 hours later to have a skin reaction read, and no reader variability. What it cannot do is equally important. A positive result means the immune system has encountered tuberculosis at some point; it does not distinguish latent infection, where bacteria are present but dormant and the person is well and not infectious, from active disease. That distinction requires symptoms, a chest X-ray, and sputum or tissue testing. Latent infection is extremely common in India, so a positive IGRA in an otherwise well person is not a diagnosis of tuberculosis.

Why take this test?

An IGRA is advised chiefly for detecting latent tuberculosis infection where that matters clinically: before starting immunosuppressive treatment such as biologics for rheumatoid arthritis or inflammatory bowel disease, before organ transplantation, in people with HIV, in those on long-term steroids, and in healthcare workers or household contacts of someone with active tuberculosis. In each case the point is to identify dormant infection that could reactivate once the immune system is suppressed, so that preventive treatment can be given first. It is also used where the Mantoux test would be hard to interpret because of BCG vaccination, or where a return visit is impractical. It is not a good test for diagnosing active tuberculosis, and a negative result does not exclude it: anyone with a persistent cough for more than two or three weeks, fever, night sweats or weight loss needs a chest X-ray and sputum testing, not a blood test alone.

• Before biologics, long-term steroids or other immunosuppression
• Before organ transplantation
• In people living with HIV
• Household or close contact of someone with active tuberculosis
• Healthcare worker screening
• Where BCG vaccination makes a Mantoux result hard to interpret

FAQs: IGRAS (Gamma Interfection) TB Gold in Dehradun