White Coat Black Art·The Dose

As experts call for more rapid tests, how accurate are they and when should you use them?

Canadian doctors and experts say rapid testing could play a bigger role in controlling the pandemic in this country, especially if rapid antigen tests were used in settings like schools, northern communities and workplaces where outbreaks are a concern.

Though not as accurate as PCR tests, rapid antigen tests could help mitigate outbreaks in places like schools

A COVID-19 rapid test device is displayed at a pop-up COVID-19 testing site. Though PCR tests, which are commonly used in Canada, are considered more accurate than rapid antigen tests, the latter can produce a result in about 15 minutes. (Andrew Vaughan/The Canadian Press)

With the fourth wave raging in many parts of Canada, some groups have been trying to implement another tool in the fight against COVID-19: rapid testing

Canada has yet to make rapid antigen tests widely and cheaply available. 

Dr. Fatima Kakkar, a pediatric infectious disease specialist and doctor at the Centre Hospitalier Universitaire Sainte-Justine in Montreal said rapid testing could play a bigger role in controlling the pandemic in Canada. 

What's the difference between PCR tests and rapid tests? 

Kakkar, also an associate professor of pediatrics at the University of Montreal, said polymerase chain reaction (PCR) tests, which are considered the "gold standard" in testing for COVID-19, look at viral RNA.

"It's able to pick up even traces of the virus," Kakkar told Brian Goldman, host of White Coat, Black Art and The Dose.

Although PCR tests can be done in as quickly as an hour in urgent situations, labs often batch samples every eight or 12 hours, causing delays of up to 48 hours before results are available.

A woman wears a face mask as she walks past a COVID-19 rapid testing business in Montreal on Sept. 12, 2021. Although PCR tests can be done in as quickly as an hour in urgent situations, labs often batch samples causing delays of up to 48 hours to get results.  (Graham Hughes/The Canadian Press)

Rapid antigen tests, on the other hand, look for pieces of protein made by the virus. Like the PCR test, a rapid antigen test involves a nasal swab, but it doesn't need to go as deep as the PCR test swab. 

In some test kits, the swab goes into a vial of liquid for about 15 minutes, and is then applied to a test strip. If there's enough protein to react with the antibodies, a coloured stripe appears, similar to the way a pregnancy test works. 

How accurate are they?

Kakkar said rapid tests are not as accurate as PCR tests, which are highly sensitive and can produce positive results even after a person is no longer infectious. 

Rapid tests are most accurate when used by people with COVID-19 symptoms in places with a lot of community spread. Under those conditions, a rapid test produces correct results 80 to 90 per cent of the time, she said. 

People who are asymptomatic or in the early stages of infection may not have a lot of viral protein in their system, which Kakkar said could result in a false negative. Under those conditions, she said the positivity rate ranges from 35 to 50 per cent, meaning 50 per cent of the time the test may not detect the infection. 

WATCH | Toronto parents spearhead rapid COVID-19 testing program:

Toronto parents organize rapid COVID-19 testing for school

2 years ago
Duration 1:56
Featured VideoA group of Toronto parents have spearheaded a rapid COVID-19 testing program for their children’s school because there wasn’t a provincial system in place.

When are rapid tests most useful?

Kakkar said high-risk settings such as hospitals can't take the chance of false negatives. And since rapid tests are most useful among people with symptoms, widespread asymptomatic testing in places like schools runs the risk of too many false positives.

In a school where there's concern about an outbreak, however, rapid testing could help — especially at times of the year when other viruses are circulating. 

When a child comes down with a fever or runny nose, Kakkar said taking a PCR test can be disruptive because it requires a day or two off from school or work while waiting for results. Families of children in the same class also want to know results quickly.

"I do sense that there is some reluctance to disclose symptoms and to be so vigilant about the symptoms simply because people are saying, 'You know what? It's another cold, it's another cold, it's another cold,' " she said. 

According to Kakkar, quick and easy rapid tests would lead to more frequent testing. It would be especially helpful in northern and remote communities, in schools, workplaces and congregate settings such as weddings and sporting events. 

How should they be used for unvaccinated people in workplaces? 

Kakkar said the use of rapid testing for unvaccinated workers depends on the risk of the work environment. In Quebec, for example, unvaccinated people cannot work in the health system.

"Being a health-care provider among immunocompromised and fragile patients, it's too much of a risk," she said. "We can't take that 10 or 20 per cent chance that we would have a false negative." 

In an office of healthy people where most are vaccinated, Kakkar said rapid testing may be helpful. She cautioned that rapid testing is not an effective substitute for vaccination, but simply an added measure to enhance workplace safety.   

How accessible are rapid tests across Canada right now? 

Kakkar said rapid testing is heavily regulated in Canada. 

"Some schools are getting it, some workplaces are getting it," she said. "But practically speaking, it's not quite so simple for an individual to just go to a pharmacy and get a rapid test."

Rapid tests rely on viral proteins in a sample to provide a positive or negative result. (Charles Contant/CBC/Radio-Canada)

She said rapid testing is more readily available in other countries, including the United States. In the U.K. and Germany, free rapid tests are available from the government through the mail and at pharmacies.

Kakkar said part of the issues is that Health Canada has not approved very many brands of rapid tests. The cost, between $40 and $75, can also be prohibitive, especially for a family with several children, she said.

David Juncker, a professor and department chair in biomedical engineering at McGill University, said with the exception of Nova Scotia, he's seen widespread reluctance to use rapid tests among Canadian provinces since the early days of the pandemic. 

He said that in his opinion, there's no good scientific reason for that provincial reluctance. "They prefer to use PCR tests and they were betting on vaccines fairly early on, which unfortunately didn't fully realize their hopes." 

Although Canada began procuring large numbers of rapid tests in September 2020 and distributing them to the provinces, Juncker said the federal government still lacks an overall strategy on rapid testing. He said its regulatory approval framework is part of the reason rapid tests aren't widely available here. 

In Juncker's opinion, the regulatory barriers are high and outright misguided. He said that when he checked back in May, many manufacturers weren't even applying to have their tests approved. "And the ones that apply, they fail."

Health Canada's own figures indicate that the federal government has distributed over 40 million tests to provinces and territories as of Sept. 2, 2021. Provinces and territories have reported using only slightly more than nine million of those tests to date. 

In an email, Health Canada said it has authorized over 50 different COVID-19 tests, including four self-testing devices. The department is continuing to review new testing options. 

Dr. Kakkar said she hopes to see rapid tests become more widely available in the weeks ahead. 

"My gut feeling is these next few weeks, we're going to continue to surge with all of these other viruses," she said. "Telling COVID apart from everything else is going to become almost a weekly, bi-weekly event." 

Written by Rachel Sanders