EXPLAINER: How do rapid molecular COVID-19 tests work?

Over the course of the pandemic, the most commonly used COVID-19 tests have been molecular PCR and rapid antigen tests. But Health Canada also approved a rapid molecular test back in the fall of 2020 that has not yet been widely rolled out in Ontario.

Abbott ID NOW rapid tests are mainly being used in rural and remote areas of the province. They are the type of test that will prove useful if Ontario implements a “test and treat” program through pharmacies  — allowing pharmacists to test people for COVID-19 and if positive and eligible, prescribe antiviral therapeutic pills right away.

How does a rapid molecular test detect COVID-19?

Infectious disease physician Dr. Alon Vaisman explains that the ID NOW test and lab PCR tests are both Nucleic Acid Amplification Tests (NAAT).

They detect COVID-19 by picking up the genetic material or RNA of the virus in the test sample.

During processing, the material is amplified or copied many times over, enabling the testing apparatus to detect even very small amounts of RNA in a sample.

Rapid Antigen Tests (RAT) on the other hand are sensitive to virus particles, like the spike protein on SARS-CoV-2 — the virus that causes COVID-19.

How accurate is a rapid molecular test?

Vaisman says NAATs are highly accurate in pinpointing the presence of the virus’ RNA in a sample.

“When you think about accuracy when it comes to tests, one way to think about it is sensitivity and specificity. In other words, how likely are you to have a false negative or a false positive? The sensitivity of the molecular tests is … perhaps somewhere between 80 to 90 per cent more than what you would expect from an antigen test. The specificity from a molecular test is very high as well — it’s around 99 per cent specific. In other words, if [the test is positive] you’re very likely to actually be picking up COVID.”

Rapid molecular tests are comparable in accuracy to PCR tests analyzed in a lab and like them, also have the potential to detect genetic material from an older infection, even if the person is not currently infected with COVID

“It’s not of as much interest to know that somebody recently had COVID as it is to know that they currently have COVID. That’s one advantage of the Rapid Antigen Test, which generally speaking picks up [the virus] only during the period of infectivity, while they’re having the disease,” explained Vaisman.

How is a rapid molecular test conducted?

Samples for a rapid molecular test are collected using a throat, nasal or nasopharyngeal (deep nasal) swab.

The ID NOW test kit includes a portable analyzing unit and can process tests at the point of care, like in a clinic or pharmacy and return results in less than 15 minutes.

Dr. Vaisman says using the machine does not require a large amount of training and a professional like a pharmacist can easily administer it.

“Essentially, it does the extraction and the nucleic amplification all within a few minutes inside the machine itself in a far more simplified process than would be done in a lab,” he said.

What are the advantages/disadvantages over lab PCR tests?

Speed, ease of use and — if made widely available — accessibility are among the main advantages of rapid molecular tests like ID NOW. Samples do not need to be sent to a second location and the facility that uses them serves as a one-stop COVID-19 testing shop.

However a single analyzer unit can only process about three to four tests an hour, meaning it could potentially process 24 to 32 tests on an average work day, if conducted in rapid succession. Comparatively, labs can collectively process thousands of samples daily.

“You could do a gigantic volume doing the standard PCR testing in a lab compared to just this machine. You have an economy of scale when you centralize PCR testing in gigantic labs … where you’re collecting samples from a wide variety of clinics and hospitals in the area, and you are centralizing the expertise and doing it very quickly,” said Dr. Vaisman. “If you use a rapid test model, you would have to purchase several of these machines and the volume would be much smaller.”

Vaisman says rapid molecular tests are most useful in areas that do not have easy access to testing labs — which is the strategy currently being used in Ontario.

Testing criteria in the province remain narrow, with only those at the highest risk and presenting symptoms currently eligible.

CityNews reached out to the Ministry of Health to find out if there are plans to make the tests more widely available to improve speed and accessibility for those eligible, but did not receive a response at the time of publishing.