IgG Anti-Coronavirus Nucleocapsid Protein Antibody (Serum/Plasma)
This test measures the presence of antibodies to the nucleocapsid protein of a coronavirus, which may indicate prior infection with the virus responsible for COVID-19.
["This test helps determine if you’ve had an infection with the virus that causes COVID-19 in the past."]
Key facts at a glance
- LOINC
- 9709-7
- Short code
- QFEV2G
- Synonyms
- C burnet Ph2 IgG Titr Ser
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top vacutainer tube
- Units
- N/A
- Ref low
- 0
- Ref high
- 1
- Critical range
- — – 800 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Immunofluorescence Assay (IFA)
- CPT
- 86638
- SNOMED
- 1221000175104
- Specimen volume
- 1 mL serum (minimum 0.5 mL)
- Stability
- Stable for 7 days at 2-8°C; for extended storage, freeze at -20°C or below for up to 4 weeks. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 48–96 hours
- Order
- routine
What This Test Measures
The test detects IgG antibodies specific to the nucleocapsid protein of the virus. IgG antibodies are a type of immune protein your body produces in response to infection. If these antibodies are present, it suggests your immune system has recognized and fought off the virus at some point.
Why It’s Done
Doctors may order this test to assess whether you’ve had COVID-19, even if you didn’t experience symptoms or had mild symptoms. It can also be used in research or epidemiological studies to track virus exposure.
Sample Collection
A blood sample is taken from a vein in your arm. You may feel a small pinch when the needle is inserted, but the procedure is quick and usually not painful. The blood is then sent to a lab for testing.
What to Expect After Testing
After your blood is drawn, you may experience mild bruising, soreness, or swelling at the injection site. Apply gentle pressure to the area to help reduce discomfort. Most people return to their normal activities immediately.
Reference range
Titer <1:200 (Negative). Phase 2 IgG titers between 1:200 and 1:800 suggest past exposure or early infection; titers ≥1:800 are highly suggestive of acute Q fever infection when combined with clinical findings.N/A
No special patient preparation required. Fasting is not necessary. Inform the ordering physician of any recent antibiotic use, particularly doxycycline or other tetracyclines, as early treatment may affect antibody titers.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
IgG Anti-N Antibody
Frequently asked questions
How long do IgG antibodies remain in the system after infection?
Can this test differentiate between different coronaviruses?
What does a positive result mean?
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