At-home coronavirus screening has become a way of life for many Californians, but some medical experts are now cautioning that one test may not be enough to determine whether someone is infected.
Health officials stress that at-home tests are a vital and accurate way of tracking COVID-19 infections but an initial negative test doesn’t mean people are out of the woods. The U.S. Food and Drug Administration suggested last week that those checking to determine whether they are infected should use multiple tests over a period of days. “When you perform an at-home COVID-19 antigen test(抗原检测) and you get a positive result, the results are typically accurate,” government officials wrote in a public statement. “However, if you perform an at-home COVID-19 antigen test, you could get a false negative result.”
Because of this, the agency “recommends repeat testing following a negative result, whether or not you have COVID-19 symptoms.” “If your first home antigen test is negative, we recommend repeating it in 24 to 48 hours,” Dr. Ralph Gonzales, a UC San Francisco associate dean, said during a recent campus town hall. Gonzales said he has noticed an additional time lag(时间差) in how long it takes a rapid test to turn positive following the beginning of symptoms—especially early on. Some people aren’t testing positive using rapid tests until four or five days after they start to show symptoms, according to UC San Francisco infectious diseases expert Dr. Peter Chin-Hong. “That’s very common these days,” he said.
At-home COVID-19 rapid tests are expected to detect a coronavirus infection at least 80% of the time, according to the FDA. By contrast, a lab-based PCR test is generally expected to detect the virus 95% of the time someone is infected. But PCR tests can take a day or longer to process, while rapid test results are available within 15 minutes. If you have COVID-19 symptoms and get a negative rapid test result, the FDA suggests testing again 48 hours later. If the second test is negative and you’re still concerned your symptoms are caused by COVID-19, the FDA suggests either a third rapid test or a lab-based PCR test.
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