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Amid widespread criticism of Canada’s COVID-19 testing strategy, experts say health agencies should look towards a widely used method to determine who has been infected and who hasn’t: blood tests.

Serological tests, or blood tests, can identify whether a person has been exposed to a particular pathogen, like the new coronavirus, by looking at their immune response, Dawn Bowdish, Canada Research Chair in aging and immunity at McMaster University, said.

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And while the tests can’t detect early infections, they could identify asymptomatic cases or people who had mild infections but were never diagnosed — filling in the gaps to help create a better understanding of Canada’s epidemic, Bowdish said.

“They are absolutely the gold standard for understanding the spread of this infection,” she said.

When the COVID-19 outbreak ends, researchers across the country will look to see how many people were truly infected with the virus to help better plan for the next outbreak. Blood tests “are extremely important” for this modelling, according to Bowdish.

McMaster University, Sinai Health, the University of Toronto and other research labs are all working to develop a blood test that can determine who is immune to COVID-19.

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Private companies, meanwhile, have already created rapid blood tests that can provide results in under 20 minutes. The tests have been approved for use in Europe, Asia and the U.S, but in Canada, they are still “under review.”

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BTNX Inc., based in Markham, Ont., has already shipped more than 20,000 rapid tests to hospitals in the U.S. and is looking to move another 200,000 to the States and the U.K.

“We are not sure when we will be able to sell in Canada anytime soon,” Mitchell Pittaway, the company’s chief financial officer, told Global News. “We are looking to have production shifted to the U.S., where we are aiming to produce over a half-million tests a week.”

BTNX Inc. said the tests sell for roughly US$10 and use just a drop of blood to determine whether someone has been infected with SARS-CoV-2, the virus that causes COVID-19.

READ MORE: How rapid testing kits could lead to more targeted screenings

Pittaway said the tests could help get Canadians back to work faster, as they could help determine if a person has developed certain antibodies that could protect against reinfection.

“[Health Canada] won’t be issuing, at this point, any approval for serological [tests] like ours until there is greater national strategy,” he said, noting that the company spoke with the federal health agency on Tuesday.

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Health Canada said in a statement that serological testing is being “prioritized for review” by the federal agency but didn’t offer a timeline on when the tests might be available.

“The department is working with the National Microbiology Laboratory to validate testing and research, along with expert advice, so that we can have confidence in the test results,” Health Canada spokesperson Geoffroy Legault-Thivierge said in an email.

He noted the tests aren’t recommended for clinical diagnosis because they don’t test for the actual virus.

“It is envisioned that pilot studies and then larger scale studies will be conducted to investigate the immunity within health care workers and other select populations,” Legault-Thivierge said.

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Prime Minister Justin Trudeau was pressed about serological testing this week and said it’s being looked at “very carefully.”

“We’re still in the early days of reflecting not just on the medical implications but on the societal implications of those tests as well, Trudeau said during his daily briefing Tuesday. “But we are continuing to pursue every avenue as a way of getting us through this.”​

Meanwhile, the U.S. Centers for Disease Control and Prevention (CDC) is using blood tests to find undetected cases, and the FDA is allowing the test kits to be used by health-care professionals.

“Quite soon, we’re going to have to start figuring out ways to get people back to work, and hopefully [these tests] have an implication in that,” he said, noting that 3.1 million Canadians either lost their jobs or had their hours slashed last month due to COVID-19.

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Infection control epidemiologist Colin Furness said there is “no reason” why Canada shouldn’t be using blood testing and that the tests could provide more clues about who is immune to the virus.

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“Our whole acute health-care system has been re-engineered to deal with COVID-19 pandemic. It may just be that we haven’t taken a step back yet to understand the big picture,” he said. “It may just be a little of the tyranny of the urgent.”

Furness said it’s “disappointing” Canada isn’t using its own domestically sourced rapid blood tests but said there are always concerns about new tests and false positives.

“It’s not about ending the outbreak,” he said. “It’s about coming to terms with what we’re actually dealing with the virus and asymptomatic transmission.”