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SARS-CoV-2 Nucleocapsid Antigen

Published: July 27, 2026Updated: August 25, 2026

This biomarker measures the presence of the nucleocapsid protein of SARS-CoV-2, the virus responsible for COVID-19, in a patient's sample.

Quick summary

Diagnostic tool for detecting the SARS-CoV-2 nucleocapsid protein.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
index
Clinical utility
diagnostic
Result kind
qualitative
FDA-cleared
Roche SARS-CoV-2 Antigen, Abbott SARS-CoV-2 Antigen
interpretation: {"text":"Index value above 0.5 indicates the presence of SARS-CoV-2 nucleocapsid antigen, suggesting active COVID-19 infection.","label":"Positive"}; {"text":"Index value below or equal to 0.5 suggests the absence of detectable levels of the SARS-CoV-2 nucleocapsid antigen.","label":"Negative"}

The SARS-CoV-2 Nucleocapsid Antigen test is designed to identify the presence of the nucleocapsid protein, which is a structural protein of the virus. This test is crucial for the rapid diagnosis of COVID-19, especially in the early stages of infection when the viral load is high.

The test is typically performed on respiratory samples, such as nasopharyngeal swabs or sputum. A positive result indicates active infection, while a negative result does not rule out infection and may require confirmation with other testing methods.

The reference range for this biomarker is 0–0.5 index, with values above this range indicating a positive result for the presence of the SARS-CoV-2 nucleocapsid antigen.

Frequently asked questions

What is the purpose of the SARS-CoV-2 Nucleocapsid Antigen test?
The test is used to diagnose active COVID-19 infection by detecting the nucleocapsid protein of the virus.
What does a positive result mean?
A positive result indicates the presence of the SARS-CoV-2 nucleocapsid antigen, suggesting an active COVID-19 infection.
  1. 1
    CDC: COVID-19 TestingSource
  2. 2
    WHO: Laboratory testing for 2019 novel coronavirus (2019-nCoV) in suspected human casesSource

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 25, 2026. · Read our editorial policy