What You Need to Know About the Results of the COVID-19 Antibody Blood Test

Antibodies also called Immunoglobulins are proteins that help fight off infections. The test looks for the COVID-19 antibodies in the blood to see if there has been an infection in the body. This handout will tell you more information about this test and the results.

What do the test results mean?

This antibody blood test can look for two types of COVID-19 antibodies, IgM and IgG.

  • Immunoglobulin G or IgG is the most common antibody. It is found in blood and other body fluids. It can help protect people against bacterial and viral infections. The IgG antibody takes time to form after an infection or immunization.
  • Immunoglobulin M or IgM is found mainly in blood and lymph fluid. This is the first antibody the body makes when it fights a new infection.

A positive IgG antibody result means:

The person who was tested might have had COVID-19 in the past, even if they did not feel sick.

  • This does not mean you are safe from getting COVID-19 again. A positive IgG antibody test does not mean you are immune to COVID-19. Doctors and scientists are not sure how long these antibodies last.

A positive IgM antibody and negative IgG antibody :

The person who was tested either:

  • Recently had COVID-19, and the body has not developed the longer-lasting IgG antibody.


  • It is a false positive. This means the person may not have had COVID-19 because of cross-reaction. This happens when the test finds IgM antibodies that your body developed against a different virus. Cross-reaction is common with IgM antibody tests.

Repeating the test in 2-4 weeks may be recommended to see if the IgG antibody appears. This second test will see if there are longer-lasting antibodies against COVID-19.

If there were a negative IgM and negative IgG on a COVID-19 antibody test, and no symptoms:

  • The person tested never had COVID-19. And, they may get it in the future.
  • The person tested had COVID-19 but never developed antibodies. This happens in some people.

This test does not show if there are symptoms of the COVID-19. If you, or your child, have any of the symptoms listed below, please talk to someone on the care team about being tested for the active COVID-19 infection:

  • Fever
  • Chills
  • Cough
  • Shortness of breath
  • Severe fatigue or muscle aches
  • Sore Throat
  • Loss of smell and/or taste
  • Runny nose/ congestion
  • Sneezing
  • Headache
  • Diarrhea
  • Nausea
  • Vomiting

We recommend that everyone continue to wash their hands, social distance, and stay home. This helps protect against COVID-19.


The Food and Drug Administration (FDA) is responsible for protecting the public health by assuring the safety, efficacy, and security of drugs, biological products, and medical devices. The Food and Drug Administration has been notified of this test, which has been validated and developed by Stanford Clinical Lab.

Please note this test has not been reviewed or approved by the FDA so:

  • Negative results do not rule out SARS-CoV-2 (COVID-19) infection.
  • Follow-up testing with a molecular diagnostic test (e.g., PCR) should be considered to rule out infection if indicated.
  • This antibody test result should not be used as the sole basis to diagnose or exclude SARS-CoV-2 (COVID-19) infection or to inform infection status.
  • Positive results may be due to past or present infection with non-SARS-CoV-2 (COVID-19) coronavirus strains, such as coronavirus HKU1, NL63, OC43, or 229E.

Author: SCH Command Center

Health Literacy Approved: The Office of Patient/Family Education & Health Literacy