TB Blood Test (IGRA – Tuberculosis Screening)

The TB Blood Test (IGRA) checks whether you have ever been infected with tuberculosis (TB). It is often requested by employers and occupational health teams, particularly for healthcare workers. It is also recommended for people who have been in close contact with someone with active TB, people who have lived in or are travelling to countries where TB is common, and people with a weakened immune system or who are about to start treatment that affects it.

The test needs just one blood sample and one visit. Unlike the older TB skin test, it does not require a return visit for reading, and the result is not affected by a previous BCG vaccination, so it avoids the false positives the skin test can give.

How the test works

In the laboratory, your blood is exposed to proteins found only in the TB bacterium. If your immune system has met TB before, your white blood cells respond by releasing a substance called interferon-gamma. The test measures this response. It is known as an interferon-gamma release assay (IGRA).

Why it matters

Finding TB infection early means it can be treated before it causes illness or spreads to others. A positive result shows that you have been infected with TB at some point, but it cannot tell whether the infection is latent (inactive, causing no symptoms and not infectious) or active. If your result is positive, you will need further assessment by your GP or a TB clinic, usually including a chest X-ray, to decide whether you need treatment. A negative result means TB infection is unlikely, although a very recent infection may not show up yet.

• Interferon-gamma (IFN-γ) response to TB-specific antigens

No special preparation required.

For blood tests, we recommend drinking plenty of water beforehand to ensure smooth sample collection. If you are taking any regular medication, continue to do so unless advised otherwise by your doctor.