SARS-CoV-2 Nucleocapsid Protein Qualitative Immunoassay (Serum/Plasma)

What This Test Measures

The test detects antibodies (immunoglobulins) against the nucleocapsid protein of SARS-CoV-2, a viral protein found in the virus’s core. These antibodies develop after the body has encountered the virus, typically within days to weeks after infection. This test is qualitative, meaning it only provides a positive or negative result—not a precise amount of antibodies.

How the Test Works

The test uses an immunoassay method (likely chemiluminescent or fluorescence-based) to detect antibodies in your serum or plasma. A small sample is analyzed to see if it reacts with the nucleocapsid protein, indicating prior exposure.

Why It’s Done

Healthcare providers may order this test to confirm past COVID-19 infection in individuals who have recovered, have mild symptoms, or are part of research studies. It’s not typically used for active infection diagnosis (for that, antigen or PCR tests are preferred).

Limitations and Considerations

This test may not detect antibodies immediately after infection (antibodies take time to develop). False negatives can occur if testing is done too early. It also may not distinguish between different variants of SARS-CoV-2. False positives are rare but possible with cross-reactions to other coronaviruses.