Conducting COVID-19 Serology Testing at PHO

Serology testing examines a person’s blood to see if they have antibodies to COVID-19. Antibodies are produced by the immune system in response to infection by bacteria and viruses. Antibody testing that is specific for COVID-19 antibodies is therefore a useful way to find out whether a person has been exposed to the virus. In contrast, PCR testing (also known as polymerase chain reaction), is a type of test that tells us if someone currently has COVID-19. Find out more about the difference between these two types of tests and their application.

At an individual level, antibodies may assist in understanding if someone had COVID-19. However, not enough is known currently about COVID-19 immunity to determine if the antibody response indicates whether a person is immune to COVID-19 and, if it does, how much immunity that provides and for how long.

Applications of Serology

Clinical Serology

Due to significant gaps in the understanding of the COVID-19 immune response, serology testing currently has very limited clinical value for individual patients.

The current uses of COVID-19 serology testing are:

  • in the investigation of suspected cases of Multisystem Inflammatory Syndrome in Children (MIS-C)
  • and with advance PHO microbiologist approval, serology may be considered in patients with severe illness who have tested repeatedly negative by PCR and where serology results would be a helpful adjunctive tool for clinical/public health action and decision making

Healthcare providers who are looking to order antibody testing for one of these purposes should consult our COVID-19 Serology Test Information Sheet. 

Serology testing should NOT be used for:

  • the diagnosis of acute infection or determining if a patient is infectious
  • determining immune status of the patient


Another application for COVID-19 serology testing is called serosurveillance, where a large number of blood samples representative of the population are collected and tested for COVID-19 antibodies to better understand which groups in the population have been infected, and to what degree. Serosurveillance helps inform the public health response and helps us better understand:

  • the true infection rate
  • which age groups were most infected
  • geographic hotspots (where it was concentrated)
  • settings which were particularly impacted
  • the level of infection over time, if repeated serosurveys are conducted

Early pandemic, PHO conducted serosurveilliance to better understand what proportion of the Ontario populations had COVID-19 antibodies to help identify hot spots and high risk groups. To find out more, please check out our Serosurveillance Initiative webpage.

Health Care Providers

See our COVID-19 Serology Test Information Sheet for details about collecting and submitting a sample and our COVID-19 Laboratory Testing Frequently Asked Questions


PHO Rounds: Novel Disease Surveillance Tools for the Next Pandemic

This seminar will introduce the concept of informal disease event monitoring systems and how this type of data can and has been used to explore communicable disease epidemiological trends among forcibly displaced persons worldwide. 

See the Event Details
Updated 30 June 2021