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Tuberculosis Infection Screening via Interferon-Gamma Release Assay (IGRA) on Whole Blood

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

This test checks for signs of tuberculosis (TB) infection by measuring your immune system’s response to TB bacteria. It’s a blood draw test often used when you’ve had contact with someone who may have TB or when symptoms suggest TB exposure.

Quick summary

["IGRA helps determine if TB bacteria are present in your body, even if you don’t have active symptoms."]

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

Key facts at a glance

LOINC
53704-3
Short code
M bovis tuberc - control IFN-g Bld-aCnc
Synonyms
M bovis tuberc - control IFN-g Bld-aCnc
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 two TB-specific proteins. If your immune system has been exposed to TB bacteria, it releases interferon-gamma—a protein that signals an active immune response. A lab detects this release to confirm infection.

What to Expect Before the Test

No special preparation is needed. You may have mild bruising or soreness at the blood draw site, but this usually fades quickly. If you’re on blood-thinning medication, let your provider know before the test.

Possible Results and Next Steps

A positive result suggests possible TB infection, but it doesn’t always mean active disease. Your doctor will discuss next steps, which may include additional testing or follow-up care. A negative result means no detectable immune response to TB proteins.

Common Causes of False Results

False positives or negatives can occur due to recent vaccination with BCG (a TB vaccine), exposure to non-TB mycobacteria, or immune conditions. Your doctor will interpret results in the context of your medical history and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IGRA Blood Test

Frequently asked questions

Why was I asked to take this test?
Your doctor may recommend this test if you’ve had contact with someone diagnosed with TB, live in a region with higher TB rates, or show symptoms like persistent cough, fever, or weight loss. It’s also used for screening in certain populations, like healthcare workers or travelers.
What does a positive result mean for my health?
A positive result means your immune system has detected TB bacteria, but it doesn’t always mean you’re sick now. You may need further testing to check for active TB or receive preventive treatment to stop the infection from developing.
Can I still get TB if my IGRA test is negative?
Yes, a negative IGRA test means your immune system hasn’t detected TB proteins at the time of testing. However, TB bacteria can still be present without causing symptoms. If you’ve had exposure, continue monitoring with your doctor.
  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