Not all COVID tests are created equal


With the increase in vaccination rates, we have every reason to hope that we are in a different era of COVID-19 than that of last winter. However, with the introduction of the omicron, a new variant that we don’t yet understand, and more time indoors, there is a potential for a harsh winter as we move into the colder months.

Medical laboratory tests will be essential to keeping our community safe this winter. Discussions are ongoing regarding the difference between rapid antigen testing and polymerase chain reaction (PCR) diagnostics performed in our laboratories. Suggestions that the PCR test be withdrawn as a requirement to return to Canada. Our collective health depends on understanding science.

Rapid antigenic tests are primarily used as a screening test, with results provided within 15 minutes.

These have been deployed across the province for use by visitors to long-term care homes; children and teachers in schools and daycares; so that unvaccinated staff can continue to work; and more. Rapid antigenic tests detect protein particles specific to the COVID-19 virus.

PCR tests are the gold standard for COVID-19 testing. Instead of a protein particle, these tests use a polymerase chain reaction (PCR) to identify the genetic material (RNA) of the COVID-19 virus. Because this genetic material is extracted, isolated, and amplified to detect the virus, testing takes longer. Results are usually provided within 24 hours.

Due to their different scientific processes, rapid antigen and PCR tests have different degrees of precision and must be deployed for very different uses.

Results from rapid antigenic tests arrive quickly but are not as accurate as PCR tests. They are more likely to provide a false negative or positive. They are more accurate when a person is showing symptoms (virus levels are highest), so detection in people without symptoms can be difficult. They can quickly detect the presence of COVID-19 within a fixed group – for example, a daycare center. If everyone is tested and three students and an early childhood educator test positive, others are likely to have it and you can react quickly to control an outbreak.

However, because of the false negatives, they are tricky for travel. You could get a negative rapid test result, but still carry and transmit the virus at the airport, on the plane and at your destination. Although a PCR test is required to enter Canada, there are dozens of popular vacation spots around the world – including France, Italy, the UK, and the US – that only require a quick antigen test to enter.

So while you are standing in line at airport security or at the boarding gate, you could be around other people who could be carriers of the virus, having tested negative with a rapid test for antigen. Stay alert.

PCR remains the best way to determine if a person has COVID-19. This test is accurate because COVID-19 genetic material can be detected when a person is asymptomatic, actively infected, and after acute illness. When rapid tests are performed anywhere, sometimes by the patient themselves, PCR tests are performed in the laboratory on machines regularly checked by trained medical laboratory professionals.

As we enter this third winter of COVID-19, we must keep in mind the unique uses of rapid antigen and PCR tests. They’re not the same – each has a different lead time, science process, target group, and recommended usage. They each provide a different type of information.

Seventy percent of labs entered COVID-19 with understaffing. Because PCR is the most accurate, this group remains essential for the future of our pandemic response. They need support and resources to continue this important work.

The tools are in place to help us get through this pandemic. We must do our part to keep up with public health measures and reduce unnecessary testing. Wash your hands, wear your masks, and keep your circles tight. We will get out of this.

Michelle Hoad is CEO of the Medical Laboratory Professionals’ Association of Ontario.


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