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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