Conducting COVID-19 Serology Testing at PHO

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

Serosurveillance

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.