Comprehensive Patient Guide to the Blood Glucose Test and Important Clinical Context for Your Upcoming Laboratory Visit
A blood test that measures your body's T-cell immune response to SARS-CoV-2 (the virus that causes COVID-19).
{"This test checks if your immune cells (T-cells) respond to COVID-19","It can detect past infection or immunity from vaccination","A small blood sample is taken and sent to a laboratory for analysis","Results help determine if you have cellular immunity against COVID-19","This test is different from antibody tests that measure humoral immunity"}
Key facts at a glance
- LOINC
- 98847-7
- Short code
- SARS-CoV-2 IGRA / COVID-19 T-cell assay
- Synonyms
- SARS-CoV-2 IFN-g Lymphs Bld IA
- Category
- cardiac
- Sample
- whole-blood
- Container
- Heparinized whole blood collection tubes (green-top) or specialized SARS-CoV-2 T-cell stimulation tubes provided by the assay manufacturer
- Units
- N/A
- Ref low
- 0.15
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Immunoassay - Interferon Gamma Release Assay (IGRA) using SARS-CoV-2 antigen stimulation with enzyme-linked immunosorbent assay (ELISA) detection of interferon-gamma
- CPT
- 86408 or 86409 (immunology procedure codes)
- SNOMED
- 124058006 or 840539006
- Specimen volume
- 3-5 mL whole blood per tube (minimum 1 mL)
- Stability
- Process within 8-16 hours of collection at room temperature (20-25°C). Do not refrigerate. Transport vertically to prevent cell sedimentation.
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 24–72 hours
- Order
- routine
What is this blood glucose test and what specific health conditions can it help your doctor to identify or monitor?
The SARS-CoV-2 Interferon Gamma Release Assay (IGRA) is a blood test that measures whether your T-cells (a type of white blood cell) have been sensitized to the COVID-19 virus. When your T-cells encounter specific COVID-19 viral proteins in the test, they release interferon-gamma, which is then measured in the laboratory.
How is the blood glucose test performed and what exact steps will the lab staff follow when collecting your sample?
A healthcare professional will draw a small amount of blood from your arm, typically using a needle. The blood sample is then sent to a laboratory where it is mixed with COVID-19-specific antigens. If your T-cells have been previously exposed to the virus (either from infection or vaccination), they will recognize these antigens and release interferon-gamma, which is detected and measured by the testing equipment.
What does the result of your blood glucose test mean for your health and how will your physician discuss the values?
A positive result indicates that your T-cells have mounted an immune response to SARS-CoV-2, meaning you have been exposed to the virus (through infection or vaccination). A negative result suggests no detectable T-cell response, which could mean you have not been exposed to COVID-19 or your immune response has waned. However, test results should always be interpreted by your healthcare provider in the context of your medical history and vaccination status.
How long does it take to receive the results of your blood glucose test and are they shared through a patient portal?
Results are typically available within 2-5 days, depending on the laboratory. Your healthcare provider will contact you with the results and explain what they mean for your specific situation.
Reference range
Negative: < 0.15 IU/mL or < 0.5 IFN-gamma release index; Positive: >= 0.15 IU/mL or >= 0.5 IFN-gamma release index; Indeterminate: Borderline results requiring repeat testingN/A
No fasting required. No special preparation needed. Inform laboratory of immunosuppressive medications or recent infections. Avoid corticosteroids and immunosuppressive drugs prior to testing if possible.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
This test is useful for assessing cellular immunity to SARS-CoV-2, which is different from the antibody-mediated immunity measured by traditional COVID-19 antibody tests. It can help determine if an individual has developed T-cell immunity from previous infection or vaccination. This information may be particularly valuable for immunocompromised patients who may not produce adequate antibody responses, or for epidemiological studies to understand population immunity levels. The test should not be used to diagnose active COVID-19 infection - for that, molecular tests (PCR) or antigen tests are more appropriate.
Frequently asked questions
Do I need to fast before this test?
Is this test painful?
Can this test tell if I currently have COVID-19?
How is this different from COVID-19 antibody tests?
Will this test tell me if my COVID-19 vaccine is working?
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 16, 2026. · Read our editorial policy