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Interferon-gamma release assay (IGRA) for SARS-CoV-2 (Tuberculosis/COVID-19 cross-reactivity screening)

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

This test measures your immune response to a protein from SARS-CoV-2, the virus responsible for COVID-19. It helps determine if your body has ever been exposed to the virus, though it may not distinguish between COVID-19 and prior TB infection.

Quick summary

["Assesses past exposure to SARS-CoV-2, not current infection status."]

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

Key facts at a glance

LOINC
99772-6
Short code
SARS-CoV-2 IFN-g Bld-Imp
Synonyms
SARS-CoV-2 IFN-g Bld-Imp
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 sample is tested for interferon-gamma, a protein your immune cells release when they detect certain pathogens. The test uses a small amount of viral protein to trigger this response. If your immune system reacts, it indicates exposure to the virus.

What to Expect Before the Test

No special preparation is needed. Bring your medical records if you’ve had tuberculosis (TB) tests in the past, as results may overlap with COVID-19 exposure.

Sample Collection

A blood sample is drawn from a vein, usually in your arm. This is a quick and painless procedure. You may feel a slight pinch, but it lasts only a few seconds.

Test Results Interpretation

Results are qualitative (positive, negative, or indeterminate). A positive result suggests prior exposure to SARS-CoV-2 or TB, but it does not confirm a current infection. Follow-up testing may be needed for diagnosis.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is primarily used in high-risk populations (e.g., healthcare workers, travelers) to screen for past exposure to COVID-19. It helps guide vaccination decisions or further diagnostic steps but does not replace viral testing for active infection.

Short name

IGRA COVID-19 Screen

Frequently asked questions

Why did my doctor order this test?
Your doctor may recommend this test if you have a history of TB, are in a high-risk group for COVID-19 exposure, or need to assess immunity before procedures that could expose you to infection.
What does a positive result mean?
A positive result indicates your immune system may have encountered SARS-CoV-2 or TB in the past, but it does not prove you had COVID-19. It may require additional testing to clarify exposure history.
Can I get vaccinated after a positive result?
Yes, vaccination is still recommended. This test helps assess prior exposure but does not affect your eligibility for COVID-19 vaccines.
  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