Best practice for COVID-19 testing

It’s a question more people seem to be asking these days, in part because science now recognizes many more symptoms as possible indications of a COVID-19 infection. Testing can help answer the question, but only if it’s done carefully.

The first thing to know is there are two kinds of COVID-19 test available in Nova Scotia: PCR tests and Rapid Antigen Tests. 

The most reliable test is the PCR test. PCR tests are performed at government-operated testing sites and are the surest way to determine whether or not you have COVID-19. The challenge is that PCR tests are only available to those who meet specific criteria. To see if you qualify for a PCR test, go to the Nova Scotia Health booking website and fill out the online form.

The second test is referred to as a RAT or “Rapid Antigen Test”. For now, RATs remain widely available in Nova Scotia as the provincial government distributes them for free in various public spaces, including MLAs’ offices, Access Nova Scotia locations and libraries. 

If you test positive on a RAT, it’s close to 100 per cent certain you have COVID and you should isolate and seek follow-up care as needed. 

Unfortunately, the opposite is not true. It's become increasingly clear that negative RAT results are often unreliable. How unreliable remains a matter of debate but some studies suggest RATs produce false negatives up to 40% of the time. In other words, if you test negative, you may actually have COVID-19 and the test just didn’t pick it up. 

1. Don’t rely on a single negative result to “prove” you don’t have COVID-19. If you have symptoms or had a potential exposure, assume you have it – at least, until you’ve performed 2-3 tests, 48-72 hours apart.

2. Repeat RATs every 48-72 hours from when symptoms start. Some test users have reported having symptoms for a week or more before finally testing positive on a RAT – perhaps because it takes that long for the viral load to become detectable in those who’ve been vaccinated and/or previously infected. 

3. If/when you test positive, continue testing every two days until your symptoms are gone and avoid close contact with others until you’ve tested negative twice in a row. 

The other important way to ensure your RAT results are accurate is to use good technique when collecting your samples. When RATS were first introduced, manufacturers recommended swabbing only your nostrils. As COVID-19 mutated, that advice changed. It’s now recommended that you don’t eat or drink for 30 minutes before testing, and that you swab your cheeks, throat and nostrils to obtain a sample that gives the best chance of detecting COVID-19. For more information on how to test, as recommended by the Ontario Science Advisory Table, check out this YouTube video.

Finally, be sure to check the expiry dates on any tests you use. If you discover a test is expired, you can do an online search to determine whether its expiration date has been extended so the test is still usable. Health Canada extended the expiration dates of many commonly used RATs by six months or more. For more information, see this information paper by Ontario Health.

Whether you test positive on a RAT or PCR test, it’s a good idea to complete the Nova Scotia’s government’s online Report and Support form as soon as possible since, if you’re considered “vulnerable”, you may be eligible for treatments that will help you recover more quickly and perhaps prevent you from developing Long COVID. 

Notes

1. A PCR test is a medical test employing the polymerase chain reaction technique, frequently used to detect small quantities of DNA specific to a pathogenic agent in blood or other body fluids.

Originally published 25 May 2023. Last updated 25 May 2023.