![]() asymptomatic individuals (78 per cent vs. In the Cochrane review of rapid antigen tests, sensitivity was higher in symptomatic vs. Because you need to need a certain amount of virus to be detectable by the test, asymptomatic individuals are more likely to have either mild infections or be too early in the disease course for the test to pick them up. The other issue that can affect the sensitivity of the test is whether someone is symptomatic. So while the procedures may be daunting for people unfamiliar with them, explanatory videos of rapid tests should go a long way toward demystifying the procedure, which actually is fairly simple. If the swab gets an inadequate sample, then the test may be inconclusive or falsely negative. Reviews of various rapid antigen tests show they perform better if done in the first week of infection. Similarly, if you test too late after symptoms start, then the viral load may be decreasing and also be undetectable. But if you test too early in the course of the infection there may not be enough replicating virus in your nose for the test to detect it. The rapid antigen tests detect a protein that makes up part of the virus and can tell you whether you have an active infection. There are multiple reasons why this might happen. In other words, some people with COVID-19 do not test positive. The issue with rapid tests is an issue of sensitivity. Ideally, you would want a test to be both sensitive and specific, but practically speaking you often must sacrifice one for the other. A specific test would correctly identify everyone without COVID-19 as negative. A sensitive test would correctly identify everyone with COVID-19 as positive. ![]() But to truly evaluate their usefulness we have to look at both their sensitivity and their specificity. The fear has been that these rapid tests would be less accurate than standard PCR tests. On the surface, the appeal of these tests should be obvious, and yet their rollout here has been slow compared to other countries, especially in Europe, where they have been widely used for months. They are less expensive than PCR tests and provide results in 15 minutes. Everything you need is in the testing kit. The tests can be done anywhere and are easy to perform. Compared to going to a test centre where lineups are starting to stretch into hours-long waits, the convenience of an at-home kit is obvious. Starting this week, Quebecers are able to get rapid test kits from pharmacies so that they can test themselves at home. This article was originally posted in the Montreal Gazette
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