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Antibody to SARS-CoV-2 Nucleocapsid Protein (Serum/Plasma)

Published: August 9, 2026Updated: August 16, 2026

This test detects antibodies in your blood that your immune system produces in response to the SARS-CoV-2 virus, which causes COVID-19. It helps determine if you’ve been exposed to the virus and whether your body has mounted an immune response.

Quick summary

["This test can help identify past infection with COVID-19 by checking for antibodies to the virus’s core protein."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
26939-9
Short code
Deprecated S pneum19 Ab Ser-mCnc
Synonyms
Deprecated S pneum19 Ab Ser-mCnc
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What This Test Measures

The test looks for antibodies called immunoglobulin G (IgG) and sometimes immunoglobulin M (IgM) against the nucleocapsid protein of SARS-CoV-2. These antibodies develop after your body has encountered the virus, typically within days to weeks after infection. The presence of these antibodies suggests you may have been infected with COVID-19 at some point, even if you didn’t experience symptoms or recovered without testing.

Why It’s Done

Doctors may order this test to confirm a past COVID-19 infection, especially in individuals who tested negative initially but have symptoms suggestive of exposure. It can also be used in research, surveillance, or as part of seroprevalence studies to track virus spread in communities.

Sample Collection and Preparation

A blood sample is drawn from a vein in your arm. The blood is then processed to separate the serum or plasma, which is sent to a lab for testing. This test uses a chemiluminescent immunoassay (CLIA) method to detect antibodies with high sensitivity and accuracy.

When to Expect Results

Results are usually available within 24 to 72 hours, depending on lab processing times. Your healthcare provider will discuss the results with you and explain their meaning in the context of your health history and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

SARS-CoV-2 Nucleocapsid Antibody

Frequently asked questions

How long does it take to get antibodies after a COVID-19 infection?
Antibodies to the nucleocapsid protein usually appear within 10 to 14 days after infection, though some people may develop them sooner or later. IgM antibodies (if tested) typically peak around 2 to 3 weeks post-infection and may decline over several months. IgG antibodies tend to persist longer, often for months or years.
Can this test be used to diagnose COVID-19 right now?
No, this test is not used to diagnose active COVID-19. It detects past exposure by measuring antibodies, not the presence of the virus itself. For diagnosing current infection, tests like PCR or antigen tests are used instead.
What if my antibody levels are low or undetectable?
Low or undetectable antibody levels could mean you were infected but the immune response was weak, you tested too early after exposure, or you have a condition that affects antibody production. It may also indicate you’ve had a recent infection with a variant that evades detection by this test. Discuss your results with your healthcare provider for personalized guidance.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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 16, 2026. · Read our editorial policy