Testing for TB Infection

For TB infection, there are two recommended tests which can be used to identify such patients.

Tuberculin Skin Test (TST)

The skin test is done by injecting a small amount (0.5 ml) of TB antigens into the top layer of skin on your inner forearm. If one has ever been exposed to TB bacteria (Mycobacterium tuberculosis), there will be a reaction indicated by the development of a firm red bump (induration) >= 10 mm at the site within 2 days.

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Figure: Tuberculin Skin Test

Interferon-gamma release assay (IGRA)

IGRA is a Blood test. If one has been exposed to TB bacteria, the white blood cell in the blood will release a substance called gamma interferon when the cells are exposed to specific TB antigens.

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Figure: Interferon-gamma release assay (IGRA)

Resources:

• Latent Tuberculosis Infection Guideline
• Guideline for Programmatic Management of Tuberculosis Preventive Treatment in India

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