IGRA Test for TB
A blood test that shows whether you've been infected with TB bacteria.
Quick Summary
To detect latent TB infection, for example before some immune-suppressing treatments.
Interferon-gamma released by immune cells exposed to TB proteins.
No preparation needed.
Overview
IGRA isn't affected by BCG vaccination, unlike the skin test.
It can't tell latent from active TB.
What It Measures
Interferon-gamma response
TB infection marker.
How It's Performed
- 01
Preparation
Usually no special preparation. Tell the staff about medicines you take.
- 02
Blood sample
A small amount of blood is taken from a vein in your arm with a thin needle.
- 03
Afterwards
Press on the spot for a minute. A small bruise is common; you can go back to normal activities.
Interpreting Results & Next Steps
Discuss with Doctor
Normal ranges differ between laboratories, ages and sexes; always use the range printed on your report and ask your doctor what your results mean.
If values are High:
A positive result means TB infection; tests for active TB may follow.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Tuberculosis Screening(opens in a new tab) · MedlinePlus, US National Library of Medicine