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Interferon Gamma Release Assay (IGRA) for Mycobacterium tuberculosis (TB) detection via whole blood

Published: August 9, 2026Updated: August 16, 2026

This blood test measures your immune system’s response to a specific protein from tuberculosis bacteria. It helps determine if you’ve been exposed to TB, even if you don’t have active symptoms.

Quick summary

["A simple blood test to check for TB exposure without a skin test reaction."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
95193-9
Short code
IFN-g HLA-B35 CMV CD8 Cells # Bld FC
Synonyms
IFN-g HLA-B35 CMV CD8 Cells # Bld FC
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
flow-cytometry
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

How the Test Works

Your blood is collected and mixed with a purified protein derivative (PPD) from *Mycobacterium tuberculosis*. If your immune system has encountered TB, white blood cells release interferon gamma (IFN-γ) as part of the immune response. This release is detected and measured to confirm exposure.

What to Expect Before the Test

No special preparation is needed. You may have a slight bruise or discomfort at the blood draw site, but this is normal. Avoid alcohol or strenuous activity before testing if advised by your provider.

Common Reasons for Testing

Doctors may recommend this test if you have risk factors for TB (e.g., recent travel to high-risk areas, weakened immune system, or contact with someone diagnosed with TB). It’s also used for screening in certain populations.

Test Results and Interpretation

Results are qualitative (positive, negative, or indeterminate). A positive result suggests past exposure or infection, but active disease requires further evaluation (e.g., imaging, culture). Follow-up with your healthcare provider is essential.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

TB Skin Test Alternative (IGRA)

Frequently asked questions

Why might my doctor order this test?
Your doctor may recommend this test to assess TB exposure, especially if you have symptoms like persistent cough, fever, or weight loss, or if you’re at higher risk due to travel, healthcare work, or immune conditions.
What does a positive result mean?
A positive result indicates your immune system has likely encountered TB bacteria, but it doesn’t confirm active disease. Active TB requires additional testing, like chest X-rays or cultures, to diagnose.
Can I get TB if I have a positive IGRA result?
No, a positive IGRA result means you’ve been exposed to TB bacteria, but you may not have active TB. Active infection would require further medical evaluation to determine treatment needs.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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 16, 2026. · Read our editorial policy