Understanding Your Laboratory Test: A Patient's Guide to Testing, Preparation, and Results
This blood test measures your T-cell immune response to SARS-CoV-2 (COVID-19) by detecting interferon gamma release after stimulation with spike protein antigens.
{"Measures T-cell immunity to COVID-19, not antibodies","Requires a blood sample collected from your vein","Results indicate whether your cellular immune system has responded to the virus or vaccine","Can help assess protection in people with weak antibody responses","Results are reported as spot counts corrected for background activity"}
Key facts at a glance
- LOINC
- 99773-4
- Short code
- SARS-CoV-2 T-cell IGRA
- Synonyms
- SARSCoV2 IGRA Spike Ct bckgrd cor Bld
- Category
- cardiac
- Sample
- whole-blood
- Container
- Heparin green-top tube or dedicated T-cell collection tube (e.g., CPT tube for PBMC isolation)
- Units
- N/A
- Ref low
- 25
- Ref high
- 200
- Critical range
- — – 10000 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 18 years
- Method
- Enzyme-linked immunospot (ELISpot) assay for interferon-gamma release following SARS-CoV-2 spike protein stimulation of T-cells
- CPT
- 86408
- SNOMED
- 124153008
- Specimen volume
- 5-10 mL whole blood
- Stability
- Process within 8-24 hours of collection; PBMCs should be isolated within 24 hours for optimal results
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 72–168 hours
- Order
- routine
What is this test, and why has my healthcare provider recommended it for me?
This test, known as an Interferon Gamma Release Assay (IGRA), measures how your T-cells respond to the SARS-CoV-2 spike protein. Unlike antibody tests that measure your body's humoral immune response, this test evaluates your cellular immune response—specifically, whether your T-cells have been trained to recognize and fight the COVID-19 virus.
How does this test work, and what exactly does it measure in my body?
A blood sample is mixed with COVID-19 spike protein antigens in a laboratory. If your T-cells have been previously exposed to the virus (through infection or vaccination), they will recognize these antigens and release interferon gamma. The test measures this interferon gamma release by counting 'spot counts' that appear on a test plate. The result is corrected for background activity to ensure accuracy.
Why is this test performed, and what health conditions can it help detect or monitor?
This test may be ordered to: (1) Assess cellular immunity in individuals who have not mounted a strong antibody response after vaccination, (2) Evaluate immune status in immunocompromised patients, (3) Support research on long-term immunity, and (4) Provide additional information beyond antibody testing for comprehensive immune status assessment.
How do I prepare for this test, and are there special instructions about food, medications, or activity?
No special preparation is typically required. You should inform your healthcare provider about any immunosuppressive medications or conditions that might affect your immune response. The test requires a standard blood draw from a vein in your arm.
Understanding your results: what do my numbers mean, and when should I discuss them with my doctor?
Results are reported as spot counts after background correction. A positive result indicates that your T-cells have mounted a response to COVID-19 antigens, suggesting previous exposure (through infection or vaccination) and some level of cellular immunity. A negative result may indicate no prior exposure or a lack of detectable T-cell response. Your healthcare provider will interpret these results in the context of your vaccination history and clinical situation.
Reference range
NCBI: CK 25-200 U/LN/A
No fasting required. Collect specimen prior to any vaccination or during baseline assessment. Avoid immunosuppressive medications if possible. Inform laboratory of current COVID-19 vaccination status and date of vaccination.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test provides valuable information about cellular immunity, which may persist longer than antibody immunity in some individuals. It is particularly useful for immunocompromised patients who may not produce adequate antibody responses but may still develop T-cell immunity. The test helps healthcare providers make informed decisions about booster vaccinations and assess overall immune protection against COVID-19.
Frequently asked questions
Is this test the same as a COVID-19 antibody test?
Will this test tell me if I'm protected from COVID-19?
How long does it take to get results?
Do I need to fast before this test?
Can this test detect current COVID-19 infection?
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