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Sarscov2igranucpsidctbckgrdcorbld

Published: August 9, 2026Updated: August 17, 2026

This test measures how your T-cells respond to COVID-19 by detecting interferon gamma release after stimulation with SARS-CoV-2 nucleocapsid antigen.

Quick summary

{"Measures T-cell immune response to COVID-19","Uses whole blood sample to detect cellular immunity","Helps assess protection after infection or vaccination","Different from antibody tests that measure humoral immunity","Results indicate your body's cellular immune memory"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
99774-2
Short code
SARS-CoV-2 T-cell response; COVID-19 T-cell ELISpot; SARS-CoV-2 IFN-γ release assay
Synonyms
SARSCoV2 IGRA Nucpsid Ct bckgrd cor Bld
Category
cardiac
Sample
whole-blood
Container
Lavender top (EDTA) tube or green top (heparin) tube for whole blood collection; specialized ELISpot collection kits may be provided by reference laboratory
Units
N/A
Ref low
0
Ref high
20
Critical range
— – 10000 N/A
Fasting
false
Population
adult
Sex
all
Age range
≥ 18 years
Method
ELISpot (Enzyme-Linked Immunospot) assay - peripheral blood mononuclear cell (PBMC) stimulation with SARS-CoV-2 nucleocapsid antigen, measuring gamma interferon (IFN-γ) spot-forming cells
CPT
86408
SNOMED
124154008
Specimen volume
5-10 mL whole blood (minimum 4 mL); volume may vary by laboratory requirements
Stability
Process specimen within 24-48 hours of collection. Store and transport at room temperature (18-25°C). Do not refrigerate. Keep upright. Avoid extreme temperatures and delays.
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
72–168 hours
Order
routine

What is this test?

This test, also known as a T-cell interferon gamma release assay for COVID-19, measures your body's cellular immune response to SARS-CoV-2 (the virus that causes COVID-19). Unlike antibody tests that measure humoral immunity, this test evaluates T-cell mediated immunity, which is a different branch of the immune system.

How does it work?

A blood sample is collected and mixed with COVID-19 nucleocapsid antigen in a laboratory. If your T-cells have been previously exposed to COVID-19 (through infection or vaccination), they will recognize the antigen and release interferon gamma. The test measures this interferon gamma response to determine if your T-cells have memory of the virus.

What will the results tell me?

The results indicate whether your body has developed T-cell immune memory against COVID-19. A positive result suggests cellular immunity is present, either from a previous infection or vaccination. A negative result may indicate no prior exposure or insufficient T-cell response. This test complements antibody testing by providing a more complete picture of your immune status.

How is the sample collected?

A healthcare provider will draw a blood sample from your arm using a needle. The sample is then processed in a laboratory where it is mixed with COVID-19 antigens and incubated. After incubation, the amount of interferon gamma is measured to determine the T-cell response.

Reference range

Negative: <20 spot-forming cells (SFC) per million PBMCs; Positive: ≥20 SFC per million PBMCs (with background correction); Indeterminate: 15-19 SFC per million PBMCs. Results should be interpreted in clinical context.N/A

Specimen: whole-blood

No fasting required. Patient should inform of immunosuppressive medications, recent infections, or COVID-19 vaccination status. Avoid immunosuppressive therapy if possible prior to collection. No special dietary restrictions.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Frequently asked questions

Is this test the same as a COVID-19 antibody test?
No, this is different from antibody tests. Antibody tests measure humoral immunity (B-cell produced antibodies), while this test measures T-cell mediated cellular immunity. Both branches of the immune system work together to protect against infections.
Do I need to fast before this test?
No fasting is typically required for this test. You can eat and drink normally before your blood draw.
How long does it take to get results?
Results typically take 2-5 days, depending on the laboratory. Your healthcare provider will inform you when results are ready.
Can this test tell me if I'm currently infected with COVID-19?
No, this test does not diagnose active COVID-19 infection. It only indicates past exposure or vaccination history and your T-cell immune response. For current infection diagnosis, PCR or rapid antigen tests are used.
Will this test tell me if I'm protected from COVID-19?
A positive result indicates T-cell immune memory, which suggests some level of cellular protection. However, the exact level of protection and duration of immunity varies between individuals. This test should be interpreted alongside clinical findings and other immune markers.
  1. 1
    CDC: COVID-19 Testing OverviewSource
  2. 2
    NIH: Understanding COVID-19 TestsSource
  3. 3
    Mayo Clinic: COVID-19 Antibody and Antigen TestingSource

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 17, 2026. · Read our editorial policy