TB Gamma Interferon Release Assay (IGRA)
A simple blood test that shows how your immune system responds to the bacteria that cause tuberculosis (TB). It works by measuring the amount of gamma interferon, a protective protein, that your T-cells release when they come into contact with TB material during testing, helping your provider find out whether you have been infected.
{"Detects if you have been infected with tuberculosis (TB) bacteria","Requires a blood sample, not a skin test","Cannot distinguish between latent infection and active disease","Results are typically available within 24-48 hours","BCG vaccination does not usually affect test results"}
Key facts at a glance
- LOINC
- 64084-7
- Short code
- IGRA, QFT, QFT-Plus, TB-IGRA, IFN-γ release assay
- Synonyms
- M TB IFN-g CD4+ bckgrnd cor Bld-aCnc
- Category
- cardiac
- Sample
- whole-blood
- Container
- Heparinized whole blood collection tubes (specific TB antigen-coated tubes provided by assay manufacturer - e.g., QuantiFERON-TB Gold Plus collection tubes)
- Units
- N/A
- Ref low
- 0.35
- Ref high
- 10
- Critical range
- — – 10000 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Interferon Gamma Release Assay (IGRA) - Enzyme-linked immunosorbent assay (ELISA) measuring Mycobacterium tuberculosis-specific antigen-stimulated gamma interferon release from CD4+ T-cells, corrected for background (nil) control
- CPT
- 86480 (Interferon gamma release assay, T-cell; QuantiFERON-TB Gold Plus)
- SNOMED
- 122441002 (Tuberculosis test), 39579006 (Interferon assay), 70951006 (Mycobacterium tuberculosis infection)
- Specimen volume
- Approximately 1 mL per collection tube, with 4 tubes required per test (Nil control, TB1 antigen, TB2 antigen, Mitogen control)
- Stability
- Whole blood must be incubated within 16 hours of collection at room temperature (22°C ± 5°C). After incubation (16-24 hours), plasma can be stored at 2-8°C for up to 28 days or -20°C for longer storage. Processed plasma stable for analysis.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 24–72 hours
- Order
- routine
What is this test?
The TB Gamma Interferon Release Assay (IGRA) is a blood test that measures how your immune system responds to the bacteria that cause tuberculosis (TB). Specifically, it measures the amount of gamma interferon (a protein produced by the immune system) that is released when T-cells are exposed to TB antigens. This test helps determine whether you have been infected with Mycobacterium tuberculosis.
How is the test performed?
A healthcare provider will draw a blood sample from a vein in your arm. The blood sample is then sent to a laboratory where it is mixed with TB antigens and incubated. If you have been infected with TB, your T-cells will recognize these antigens and release gamma interferon, which is then measured. The test includes a positive control (to ensure your immune system can respond) and a negative control (to account for any background interferon).
What do the results mean?
Results are typically reported as positive, negative, or indeterminate. A positive result indicates that you have been infected with TB bacteria, but it cannot distinguish between latent TB infection (where the bacteria is dormant) and active TB disease. Additional tests, such as a chest X-ray or sputum culture, are needed to determine if you have active TB disease. A negative result suggests no TB infection, but the test may be false-negative in some cases, such as in people with weakened immune systems.
Why is this test used?
The IGRA test is often used because it is more specific than the traditional TB skin test. It is less likely to show a positive result in people who have received the BCG vaccination (used in some countries to prevent TB). The test is also preferred because it requires only one visit, and results are available faster than the TB skin test.
Reference range
Interpretation categories: Negative (<0.35 IU/mL IFN-γ), Positive (≥0.35 IU/mL IFN-γ and meeting criteria), Indeterminate (borderline results or invalid controls). Results should be interpreted in clinical context with patient risk factors.N/A
No fasting required. No special dietary restrictions. Inform laboratory of immunosuppressive medications, recent vaccinations (especially live vaccines), or conditions affecting immune function. Collect preferably in morning but not required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test is primarily used to detect latent TB infection in people who may have been exposed to TB bacteria, such as healthcare workers, people who have been in close contact with TB patients, or individuals from countries with high TB rates. It is also used for pre-employment screening and in outbreak investigations. A positive result does not necessarily mean you have active TB disease, but it indicates that further evaluation is needed to determine if treatment for latent TB infection is appropriate to prevent progression to active disease.
Frequently asked questions
Do I need to fast before this test?
Does the BCG vaccine affect the test results?
Can this test tell if I have active TB disease?
Is the test safe?
How long does it take to get results?
Sources
- 1
- 2
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