Rapid at-home [COVID] tests are a good option for people who have been exposed to the virus, who want to know whether a sore throat is Covid-19 or just a cold, or who want a little bit of extra assurance before visiting a vulnerable relative or after traveling to a virus hot spot, experts said.
People with symptoms can take a rapid antigen test immediately, experts said, but those who have had a known exposure to the virus should wait three to five days before doing so. Testing too soon, before the virus has had a chance to replicate, increases the odds of a false negative.
Rapid antigen tests are highly specific, which means that they generate relatively few false positives. However, a positive result is more likely to be a false positive when the prevalence of the virus is low; in these instances, people may want to take a second test. (The Centers for Disease Control and Prevention recommends lab-based molecular tests, like a P.C.R. test, for confirmatory testing.)
But experts recommended not waiting for the results of a second test to begin taking precautions. If you test positive, you should isolate yourself, monitor your symptoms and seek medical care if necessary.
