There are a lot of things to consider when you develop COVID-19 symptoms. Like when you should test, how long you should isolate, and how long you might test positive for. You might also be wondering how reliable at-home COVID tests really are. We were too.
So we asked two doctors — Dr. Thomas Russo, chief of the division of infectious diseases in the department of medicine at University at Buffalo, and Dr. Timothy Murphy, SUNY distinguished professor of medicine at University at Buffalo — to break down how the at-home tests work, and if they’re effective.
What’s the difference between at-home tests and PCR tests?
PCR (aka polymerase chain reaction) tests are a type of COVID-19 test that you can get from a healthcare provider. Yup, that very pleasant nose-swabbing experience. At-home tests are rapid antigen COVID tests that you can pick up at a pharmacy and take, you guessed it, at home. BTW: The FDA has a list of approved at-home tests.
PCR tests are far more sensitive than at-home tests, Dr. Murphy said, meaning they require a smaller amount of the virus from the sample to detect the virus. Since at-home tests antigen aren’t as sensitive as PCR tests, an at-home test “turns positive generally a day or two after PCR,” said Dr. Murphy. And at-home tests are more sensitive to the viral proteins (and more likely to provide an accurate result) if you have COVID-19 symptoms than if you are asymptomatic.
Got it. So are at-home COVID tests effective?
Most of the time, yes. But at-home tests aren’t as sensitive to the viral proteins as PCR tests. So if you are experiencing COVID-19 symptoms and get a negative test result from an at-home COVID test, it might not be accurate, said Dr. Russo.
Dr. Murphy said to take another test if you think you might have COVID, but got a negative test result. “Doing another test 24 hours later really increases the sensitivity of that test,” he said. That’s called serial testing. Which increases the likelihood that the test will detect if COVID-19 is present. “And you can even do it a third day,” Dr. Murphy said.
Can at-home COVID tests give false positives?
Technically yes, but it’s unlikely. “False positives —in other words, a positive test when you don't have it — are very unusual,” Dr. Murphy said. So if you take an at-home test for COVID-19 and it comes back positive, it’s very likely that you have COVID, both doctors said. So you should follow isolation and mask guidelines.
When should I take an at-home test if I have COVID symptoms?
If you have COVID symptoms, you can take an at-home test right away. If it comes back negative but you’re still experiencing symptoms (and/or were exposed to someone who tested positive for COVID-19), wait another 24 hours and take another test, Dr. Murphy said.
If you don’t have symptoms but you were exposed to someone who tested positive for COVID, the CDC recommends taking an at-home test within five days. And if you test negative after five days, take another test again in one to two more days to be extra sure.
Are at-home tests better at detecting certain variants?
Back in December, the FDA had concerns about whether or not at-home COVID tests could detect the presence of Omicron. But you can rest easy, because research has since shown that the at-home tests can detect the original COVID variant, the Delta variant, and Omicron variant.
At-home COVID-19 tests are mostly reliable. And false positive results are unlikely. But if you have symptoms and you get a negative test result, it’s fair to say “ask again later” and take another at-home test after 24 hours. And if you’re still not sure, check with your doctor or schedule a PCR test.
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