Frequently Asked Questions: COVID-19 Serology Testing

Mayo Clinic Laboratories offers a variety of serology tests to identify the presence of an antibody 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 infection?

A: Yes, Mayo Clinic Laboratories’ testing can be used to detect IgG and total (IgM/IgG/IgA) antibodies against SARS-CoV-2. 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 antibodies to SARS-CoV-2 develop approximately 8 to 11 days post-symptom onset (seroconversion) for the majority of patients. The presence of SARS-CoV-2 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 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: The full menu of COVID-19 serology tests is available to order by all Mayo Clinic Laboratories clients. Three types of antibody tests are currently offered: 

SARS-CoV-2 anti-RBD total antibody tests 

  • Methods:
    1. Roche Diagnostics ECLIA (Mayo ID: COVSQ) in serum 
      • This is a semi-quantitative test which provides results in U/mL 
      • This assay can be used for the manufacture of COVID-19 Convalescent Plasma 
    2. Thermo Fischer ELISA (Mayo ID: COVAB) on serum 
      • This is a qualitative assay 
      • This assay does not have FDA EUA for manufacture of COVID-19 Convalescent Plasma 

These tests detect total antibodies against the SARS-CoV-2 receptor binding domain (RBD) and will be positive following natural infection or after vaccination, but will not differentiate between the two events 

SARS-CoV-2 anti-NC Total Antibody Tests on serum 

  • Method:
    1. Roche Diagnostics ECLIA (Mayo ID: COVTA
      • This assay detects total antibodies against the SARS-CoV_2 nucleocapsid protein.  
      • This assay will not be positive following SARS-CoV-2 vaccination. 

SARS-CoV-2 Multi-Antigen IgG Antibody Testing on Dried Bloods 

  • Method: 
    1. Luminex xMAP assay (Mayo ID: CORBS
      • This test is validated for use from fingerstick whole blood samples collected under healthcare worker supervision. 
      • This assay detects IgG class antibodies against the NC, RBD and spike subunit 1 (S1) proteins. A positive result requires IgG reactivity to the NC antigen and one or both of the RBD and S1 antigens. Results are reported as ‘positive’ or ‘negative’ and specific antibody reactivity against the three antigens is not indicated. 

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

A: IgG or total 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 offers 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 ID: COVOO), not serology testing. 

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

Detection can indicate:

  • Prior exposure (infection) to SARS-CoV-2. 
  • The presence of an immune response to SARS-CoV-2.  

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.