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TB blood test (IGRA)

Infection and immunity tests · also printed as QuantiFERON, QFT, QuantiFERON-TB Gold, T-SPOT, T-SPOT.TB

Typical UK adult rangeExpected result: Negative

Negative is the expected result. Indeterminate results are repeated.

What this test measures

The interferon-gamma release assay (QuantiFERON or T-SPOT) measures the immune system's memory of tuberculosis bacteria. A positive means the person has met TB at some point, most often as a dormant infection rather than active disease.

Why doctors request it

Used before immune-suppressing medicines, in new entrant screening, and in contacts of people with TB. It does not tell active from latent TB.

What commonly pushes it up

Latent (dormant) TB infection
Active TB
Past TB, treated or not

What commonly pushes it down

A negative result is the usual finding

Everyday reasons for a value outside the range

Results can be equivocal and are then repeated
Recent vaccination or infection elsewhere can occasionally give a weak positive

About the sample

No fasting needed.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.

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This is an educational summary of results you uploaded. It is not medical advice, a diagnosis or a treatment plan, and it does not replace the doctor who requested the test. If you are worried, or a result is marked outside range, discuss it with your doctor. Written and reviewed by a UK consultant physician. Reference ranges vary between laboratories.