Rapid antigen tests for COVID-19 are quicker and easier, but also less accurate, than the PCR (polymerase chain reaction) tests that Canada has relied upon during the pandemic.
But as various provinces make rapid antigen tests more widely available to businesses, schools and other groups, here’s what you need to know about how to use them.
When should you take a rapid test?
Rapid tests are for people who have no symptoms of COVID-19, like coughing or fever, said Sarah Mostowich, program lead for the StaySafe Initiative, which provides rapid test kits in Waterloo Region in Ontario.
She said it’s important to note that rapid tests are generally offered as part of a frequent testing program and aren’t normally administered just once.
“This is something that should be done two to three times a week or so if you’re feeling healthy,” Mostowich said.
The idea is to use it as a screening tool, to catch whether you have COVID-19 before you potentially spread it to others in your workplace, school or other higher-risk setting, she said.
With COVID-19, people who don’t have symptoms can still transmit the virus, she said, “And so it’s really important for us to have a measure to detect and shut down asymptomatic transmission.”
“It’s not a diagnostic tool. It is a screen that people are using similar to when someone does a temperature check on you before you enter the door, similar to the symptom-screening questionnaires that you have to answer. And this is another tool to kind of rule out whether you have COVID or not.”
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If you have COVID-19 symptoms, you should report to a PCR testing centre and get that test instead, said Dr. Susy Hota, an infectious diseases specialist and medical director of infection prevention and control at the University Health Network in Toronto.
You should also get a PCR test if you have been exposed to a known case of COVID-19, she said.
Most provinces are focusing their rapid test strategies on congregate settings like long-term care homes, businesses and schools, to contain the spread of the virus in these environments, Hota said.
How do the tests work?
The tests typically come in a small kit containing a test strip, a swab, a vial of buffer solution and a test tube, Mostowich said.
“The rapid tests are really simple. It’s about two minutes or so to actually take the test. Then it takes 15 minutes to process,” she said.
First, you add some buffer solution to the test tube, then you swab inside your nostril, and put the swab into the tube, she said. Then, you swirl it around in the liquid five or 10 times, squeeze out any residual liquid from the swab and break off the top of the swab. Then, you squeeze five drops of the solution onto the test device and wait 15 minutes.
To watch Mostowich take a rapid test, click the video below.
After 15 minutes, the window of the test strip can be read a lot like a pregnancy test, she said. One line means negative and two lines mean positive.
“The rapid antigen tests are basically designed to look for a small piece of the virus that could be present if you swab the nose,” Hota said.
How are they different from other COVID-19 tests?
Compared to the PCR COVID-19 tests that you might get at a designated testing centre, these rapid antigen tests are easier to use, Hota said.
For one thing, the swab doesn’t go as far up your nose so it’s a little more comfortable, she said.
It’s also more convenient.
“It can be done at home and self-administered, which is an advantage. PCR tests, obviously, you have to go to an approved centre like an assessment centre,” she said.
You can also get results in 15 minutes after taking the test, instead of waiting up to 36 hours for a PCR test, she said.
However, PCR tests can give more information than just whether or not you have COVID-19, Mostowich said.
“Typically when you get a PCR test, there’s other components that they do – not just to diagnose COVID-19, but genome sequencing to determine which type of COVID you have.” This can be valuable information for public health, she said.
Where can you get rapid tests?
Access to rapid tests varies significantly across the country, so you should check the website of your province’s health ministry for details.
In Alberta and Ontario, you can make an appointment at Shoppers Drug Mart pharmacies to receive a rapid test, at a cost of about $40 per test.
Employers in many provinces can receive rapid test kits through various federal and provincial government initiatives and distribute them to their employees as part of a testing program.
In other provinces, including B.C. and Saskatchewan, long-term care homes and other health-care settings have rapid test programs.
In Nova Scotia and Quebec, the province has pilot rapid testing programs for school-aged children.
What should you do after you get your result?
“If you test positive on a rapid antigen test, you should immediately self-isolate and get your close contacts to do so as well,” Mostowich said. Then, she said, the individual who tested positive should get a PCR COVID-19 test as soon as possible to confirm the result.
If you test negative, you should continue to adhere to public health measures and test again in about two days to confirm you are still negative, Hota said.
“Having a negative test result is not license to go out and party,” she said.
Hota worries that people might place too much faith in rapid tests and ignore the other public health measures, like masking and distancing, that have also been shown to prevent COVID-19 transmission.
How accurate are they?
Although rapid tests are easier and more convenient, they’re not better in every way, Hota warned.
“It’s a trade-off because the PCR test is far more reliable and accurate.”
Rapid antigen tests can show false negatives, she said, meaning you might have COVID-19 even if the test says you don’t.
For this reason, rapid antigen tests should be taken more than once, Hota said – every two days or three times per week – to ensure that you don’t miss anything, or that you haven’t been infected with this virus since your last test.
“It’s also important to note that if you test negative on an antigen test, it could also be that you have COVID, but you literally just caught it,” Mostowich said. “So you’re not actually shedding a viral load that a test would detect that you have COVID.
“That’s why we advocate for serial rapid testing, because this is something that you should be doing every couple of days so that if you did have COVID but you weren’t shedding enough, then in a couple of days you would be shedding enough so that you’re detectable by a test.”
False positives can happen too though they are less common, she said, which is why you should immediately get a PCR test if you get a positive on a rapid test to confirm whether you have COVID-19.