Finding the right tests…
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TB Gold is a blood test - technically called an interferon-gamma release assay, or IGRA - that checks whether your immune system has ever encountered the bacteria that cause tuberculosis. It works by mixing a sample of your blood with TB-specific proteins and measuring the immune response, which makes it more accurate than the older Mantoux skin test in people who've had the BCG vaccine as a child, since BCG can make that skin test falsely positive. A positive TB Gold result means TB infection is present somewhere in your body - it does not by itself tell you whether that infection is latent or active disease.
The result comes back as positive, negative, or occasionally indeterminate if the sample doesn't respond properly to the lab's control reagents. A positive result confirms your immune system has been exposed to TB bacteria, but on its own it cannot separate latent infection, where the bacteria are inactive and you have no symptoms, from active TB disease, which needs different tests - a chest X-ray and a sputum test - to confirm. This distinction matters because latent and active TB are treated very differently.
A positive TB Gold result means you have been infected with TB bacteria at some point. It cannot say whether that infection is currently latent - dormant, not sick or contagious - or has progressed to active TB disease. Working that out needs a chest X-ray, and if active disease is suspected, a sputum sample checked for the bacteria directly.
Because the BCG vaccine, given routinely to infants in India, can make the older Mantoux skin test falsely positive years later, a blood-based IGRA like TB Gold avoids that pitfall - it isn't affected by prior BCG vaccination. It also needs only one visit, compared with the two the skin test requires.
- People with a known TB exposure, such as a household contact of someone with active TB - Healthcare workers as part of routine occupational screening - People about to start medicines that suppress the immune system - People with HIV, where TB screening is a standard part of care
A positive result usually leads to a chest X-ray and a review of your symptoms, to check for active disease. If both are clear, you're generally considered to have latent TB infection, which your doctor may recommend treating to prevent it becoming active later.
TB Gold is a blood test that isn't affected by a past BCG vaccination, while the Mantoux skin test can come back falsely positive in people who've had BCG, which is nearly everyone vaccinated in India as an infant. TB Gold also needs just one visit, compared to two for the skin test.
Not necessarily. It confirms you've been infected with TB bacteria at some point, but distinguishing latent infection from active disease needs a chest X-ray and, if active disease is suspected, a sputum test.
It means TB bacteria are present in your body but inactive - you have no symptoms and can't spread the infection to others. Latent TB can be treated with medicine to reduce the chance it ever becomes active disease.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Yes, occasionally the test doesn't respond properly to the lab's control samples, giving a result that's neither clearly positive nor negative. Your doctor usually repeats the test if this happens.
There's no fasting requirement for this test. Ask your doctor or the centre when you book, especially if other blood work is being done at the same time.
People with known TB exposure, healthcare workers, people with HIV, and anyone about to start immune-suppressing medicine are commonly screened, since reactivating a latent infection is a real risk in these groups. Ask your doctor whether your situation calls for screening.