TB Interferon Gamma Release Assay (IGRA)
A blood test that measures how your immune system responds to the bacteria that cause tuberculosis by detecting interferon gamma, a protein released from T-cells when they encounter TB antigens in your blood sample.
{"This test checks if you have been infected with tuberculosis (TB) bacteria","It uses a blood sample to measure how your T-cells respond to TB-specific antigens","The test can detect both latent (dormant) and active TB infection","Unlike the TB skin test, this test is not affected by BCG vaccination","Results are typically available within a few days"}
Key facts at a glance
- LOINC
- 88517-8
- Short code
- IGRA-TB, TB-IFN, QFT, T-SPOT
- Synonyms
- M TB IFN-g CD4+CD8+ bckgrnd cor Bld-aCnc
- Category
- cardiac
- Sample
- whole-blood
- Container
- Heparinized green-top tube (sodium heparin) or specific QuantiFERON-TB Gold Plus collection tubes
- Units
- N/A
- Ref low
- 0
- Ref high
- 0.35
- Critical range
- — – 10000 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 2 years
- Method
- Enzyme-linked immunosorbent assay (ELISA) or enzyme-linked immunospot assay (ELISpot) for detection of interferon-gamma release following Mycobacterium tuberculosis antigen stimulation
- CPT
- 86480
- SNOMED
- 122442009
- Specimen volume
- 3-5 mL of whole blood per tube (typically 4 tubes for QuantiFERON-TB Gold Plus: Nil, TB Antigen 1, TB Antigen 2, and Mitogen control)
- Stability
- Process within 16 hours of collection if stored at 2-25°C. Do not refrigerate. Incubate tubes within 8 hours of collection for optimal results.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 24–72 hours
- Order
- routine
What is this test?
The TB Interferon Gamma Release Assay (IGRA) is a blood test that measures how your immune system responds to the bacteria that cause tuberculosis (TB). Specifically, it detects interferon gamma, a protein released by certain T-cells (called CD4+ and CD8+ T-cells) when they encounter TB antigens in the blood sample after laboratory stimulation.
How does the test work?
A healthcare provider will draw a small amount of blood from your arm. The blood sample is then sent to a laboratory where it is mixed with TB-specific antigens. If you have been infected with TB bacteria, your T-cells will recognize these antigens and release interferon gamma. The laboratory measures the amount of interferon gamma produced to determine if your immune system has been previously exposed to TB.
What do the results mean?
A positive result means you have been infected with TB bacteria. However, this test cannot distinguish between latent TB infection (where the bacteria are dormant in your body but not causing illness) and active TB disease (where the bacteria are actively multiplying and causing symptoms). Additional tests, such as a chest X-ray or sputum culture, are needed to determine if you have active TB disease.
What are the advantages of this test?
The IGRA test has several advantages over the traditional TB skin test. It requires only one visit to the healthcare provider, results are available faster (usually within 24-48 hours), and it is not affected by prior BCG vaccination (a TB vaccine that some people received). It is also more specific for TB caused by Mycobacterium tuberculosis and less likely to give false positive results in people who have received BCG vaccination or been exposed to non-tuberculous mycobacteria.
Reference range
Interpretation: Negative (< 0.35 IU/mL or < 8 spot-forming cells per 100,000 peripheral blood mononuclear cells); Positive (≥ 0.35 IU/mL or ≥ 8 spot-forming cells); Indeterminate (borderline results requiring repeat testing)N/A
No fasting required. No special dietary restrictions. Inform laboratory of current immunosuppressive medications, recent infections, or prior TB testing. Vaccination history should be documented.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test is primarily used to diagnose Mycobacterium tuberculosis infection, including both latent TB infection and active TB disease. It is particularly useful for people who have received BCG vaccination, as it is more specific to TB-causing bacteria. The test is also valuable for screening healthcare workers, immigrants from countries with high TB prevalence, and people with weakened immune systems who are at higher risk for progressing from latent to active TB disease.
Frequently asked questions
Do I need to fast before this test?
Can this test tell if I have active TB?
Will the BCG vaccination affect my test results?
How long does it take to get results?
Is this test safe during pregnancy?
Sources
- 1
- 2
- 3LOINC Code 88517-8Source
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy