Frequently Asked Questions: COVID-19 Serology Testing

Mayo Clinic Laboratories has developed a new serology test that can be used to identify the presence of an immune response to SARS-CoV-2, the virus that causes COVID-19. The following addresses some of the most frequently asked questions about this testing.

Q: Does Mayo Clinic Laboratories currently offer a test to detect COVID-19 exposure?

A: Yes, Mayo Clinic Laboratories’ test can be used to detect IgG antibodies against SARS-CoV-2, the causative agent of COVID-19. This testing is only advised to be performed on individuals at least 10 days after initial symptom onset or at least 10 days after initial known exposure. This is because IgG antibodies to SARS-CoV-2 develop approximately 8 to 11 days post-symptom onset (seroconversion) for the majority of patients. The presence of IgG antibodies indicates that the patient has been exposed to COVID-19. 

Q: What is antibody testing?

A: Antibody testing, also known as serologic testing, is used to detect antibodies in a patient’s blood specimen (serum). Antibodies are produced by the immune system in response to an infection. The presence of antibodies indicates that an individual has been exposed to (infected with) that particular infectious agent. These antibodies can be detected in some cases for years after the individual has recovered from the infection and will also be present if the patient was never even symptomatic. Serologic tests detect antibodies against infectious agents in serum and are a marker of an immune response to infection.

Q: Who can order this test?

A: At this time, our serology test is only available to the Mayo Clinic internal practice and clients who have received prior authorization. We are continuously working to add more serology testing capacity to meet the needs of patients and providers around the world.

We are coordinating closely with state and federal officials to roll out testing guided by these priorities:

  • Protecting health care workers and using testing as a tool to get them back into the workforce, while recognizing the potential limitations of protective immunity
  • Identifying newly recovered patients with high antibody levels who can donate their antibody-rich blood, known as convalescent plasma, to potentially save other patients with severe COVID-19. Mayo Clinic is at the forefront of this national initiative.
  • Supporting research for vaccine candidates.

Q: Will this test detect antibodies in everyone who has had COVID-19?

A: IgG antibodies to SARS-CoV-2 develop approximately 8 to 11 days post-symptom onset (seroconversion) for the majority of patients. Some individuals may develop antibodies after this time frame, while others, particularly those who are immunosuppressed, may never develop a detectable immune response. 

Q: Should this test be used to diagnose patients suspected of currently having COVID-19?

Mayo Clinic Laboratories is offering serology testing only as a means to detect antibodies to the virus, not to diagnose recent or active infection. We are focusing on correct diagnostic test stewardship and utilization. 

Symptomatic patients should be tested using PCR testing (Mayo Test IDs: COVID or SARS2), not serology testing.

Q: What does detection of IgG antibodies against SARS-CoV-2 mean for a patient? 

Detection can indicate:

  • Prior exposure (infection) to the virus.
  • The presence of an immune response that suggests the patient is less likely to get infected or re-infected compared to seronegative individuals.  

Q: Is Mayo Clinic Laboratories developing a test to detect IgM and IgA antibodies against the virus?

Although IgM and IgA antibodies against the virus may be detected sooner than IgG antibodies, we will not be offering this testing for the following reasons:

  • These are often considered markers of acute infection; however, it still takes one week or longer for these antibodies to be detectable in most patients, making them limited as markers of recent infection.
  • Studies at Mayo Clinic Laboratories have shown a concerning rate of false-positive results using an IgA SARS-CoV-2 ELISA.