So what are these tests actually good for?Įven though it seems like a good idea to have everyone take a rapid COVID-19 test the day of a gathering to make sure they're negative, experts say that's not how the tests were meant to be used. "We saw a lot of variation in the sensitivity of different brands of tests and our overall results combine findings from different studies that evaluated the same tests," lead author Jacqueline Dinnes from the University of Birmingham said in a podcast about the report. Their review included 49 different kinds of tests. The same researchers also found that not all home tests were equally accurate. "Rapid antigen tests are considerably less accurate when they are used in people with no signs or symptoms of infection, but do perform better in people who have been in contact with someone who has confirmed COVID‐19," they wrote. This is also what researchers found when they took a look at more than 100 studies of antigen tests and published their findings in the Cochrane Database of Systematic Reviews this past July. If you don't have any symptoms though, don't count on antigen tests to give you a definitive answer on whether or not you're in the clear. That means antigen tests aren't all that useful for ruling out COVID-19, but they can be valuable for confirming that cold really is COVID-19. And sensitivity is how good the test is at finding the virus.Īccording to the CDC, antigen and PCR tests are both good at avoiding false positives, but PCR tests are generally more sensitive than home tests. Specificity is how good the test is at avoiding false positives. And there are two measures of test performance to know about: specificity and sensitivity. "Actually you don't want snot on the thing."Īnd while, on average, people will get a positive antigen test result around the time they become infectious, Baird says it's important to remember that there will always be plenty of people on either side of that average: those who test positive much earlier than most and those who test positive much later.īoth kinds of tests have their advantages and disadvantages. Some people even get mucus on the swab, mistakenly thinking mucus will have plenty of virus in it. "There's going to be some people who stick it in their mouth," he says, explaining that not everyone follows the testing instructions as written. After all, people doing these tests at home make mistakes and aren't trained like those who are doing COVID-19 tests in a lab. Geoffrey Baird, chair of the Department of Laboratory Medicine and Pathology at the University of Washington School of Medicine.īut Baird says perhaps the biggest factor is human error. Many factors could make it seem as though home tests are taking longer to register a positive result, such as the virus multiplying faster somewhere other than the nostrils in some patients, says Dr. But the rapid antigen tests aren't actually looking for that spike protein. That's because as the virus evolves, scientists are mainly seeing changes in its spike protein, which is what the virus uses to attack and enter healthy cells. Is the latest omicron variant tripping up at-home tests? So it's only fitting to do a reality check on what those rapid COVID-19 tests, also called antigen tests, can do - and what they can't.
But some experts caution against putting too much faith in a negative result. The virus has mutated and then mutated again, with the tests offering at least some sense of control as the Greek letters pile up. It feels like the right thing to do, right? Still, you dutifully swab your nostrils before dinner parties, wait 15 minutes for the all-clear and then text the host "negative!" before leaving your KN95 mask at home. Rapid antigen tests are ubiquitous, but some Americans have learned the hard way that a negative test result isn't necessarily the final word.Īs the COVID-19 pandemic enters its fourth year, a negative result on a little plastic at-home test feels a bit less comforting than it once did.
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