Serum or Plasma Immunoassay for Anti-SARS-CoV-2 Nucleocapsid Antibodies (Qualitative)

What Does This Test Measure?

The test looks for antibodies called anti-nucleocapsid IgG. These antibodies are part of your immune system’s defense against the SARS-CoV-2 virus. If present, they indicate that your body has recognized and reacted to the virus, suggesting prior exposure. This is different from tests for surface proteins (spike antibodies), which can appear sooner after infection.

Why Might Your Doctor Order This Test?

Your doctor may recommend this test if you’ve had symptoms of COVID-19, even if tests for the virus itself (like PCR or antigen tests) came back negative. It can also be used to confirm past infection in people who have recovered or have mild symptoms. Some healthcare providers use it to monitor immune response in vaccinated individuals or those with long COVID.

How Is This Test Performed?

A blood sample is drawn from a vein in your arm. The serum or plasma is then tested using an immunoassay method to detect the presence of anti-nucleocapsid IgG antibodies. The result is qualitative, meaning it only tells you whether antibodies are present or not.

What Are the Possible Results?

The test result will either be positive (indicating the presence of anti-nucleocapsid IgG antibodies) or negative (indicating no detectable antibodies). A positive result suggests your body has likely been exposed to the virus at some point, but it does not confirm active infection. A negative result means antibodies were not detected in this sample.