Serum or Plasma Substance Concentration by Immunoassay (e.g., Anti-Spike Protein Antibody)
This test measures the presence of antibodies against the spike protein of a virus (e.g., SARS-CoV-2) in your blood. Antibodies are your body’s immune response to infection.
["Helps track immune response to a viral infection, often used in COVID-19 testing and monitoring."]
Key facts at a glance
- LOINC
- 31968-1
- Short code
- S pneum Ag Spt Ql
- Synonyms
- S pneum Ag Spt Ql
- Category
- coagulation
- Sample
- sputum
- Container
- Sterile sputum container
- Units
- N/A
- Ref low
- 0.8
- Ref high
- 1.2
- Critical range
- — – 5 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 85610
- SNOMED
- 396252006
- Specimen volume
- 3-5 mL
- Stability
- Room temperature: 2h, Refrigerated: 24h
- TAT
- 4–24 hours
- Order
- routine
What This Test Measures
This test detects specific antibodies (IgG) produced by your immune system in response to exposure to a virus, such as the one responsible for COVID-19. These antibodies are part of your body’s defense mechanism and can indicate past infection or vaccination.
Why It’s Done
Doctors may order this test to confirm past infection, assess immune response after vaccination, or monitor recovery from a viral illness. It can also help evaluate immune status in certain medical conditions.
Sample Collection and Preparation
A blood sample is drawn from a vein, typically in your arm. The blood is processed to separate serum or plasma, which is then tested for the presence of antibodies.
What to Expect Before the Test
No special preparation is needed for this test. You may have some mild discomfort from the needle, but it usually goes away quickly. If you’re on blood-thinning medication, let your healthcare provider know before the test.
Reference range
INR: 0.8-1.2 (warfarin: 2.0-3.0)N/A
Inform your healthcare provider if you are taking blood thinners. No special preparation required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Anti-Spike Protein Antibody (IgG)
Frequently asked questions
Positive results suggest your body has developed antibodies against the virus, indicating either prior infection or vaccination. However, antibody levels can vary and may not always correlate directly with immunity or protection over time.
Negative results mean no detectable antibodies were found in this sample, which could mean you haven’t been exposed or vaccinated yet. However, it’s possible antibodies haven’t developed or have wane since exposure.
How long will I have to wait for results?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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