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'90% as sensitive': UW doctor explains accuracy of at-home COVID-19 tests

Wednesday marked the launch of the Biden administration's initiative to send free COVID-19 tests directly to Americans.

SEATTLE — Wednesday marked the launch of the Biden administration's initiative to send free COVID-19 tests directly to Americans. But just how accurate or reliable are the rapid antigen tests? UW Medicine's Dr. Geoffery Baird explained why those worried, shouldn't be.

The Biden administration has launched a website where anybody in the U.S. can sign up to have four free COVID-19 tests sent to their home. 

The tests have been in short supply for the past several months as COVID cases tied to the highly contagious omicron variant have surged and people traveled for the holiday season. 

The antigen tests being sent to Americans differ from the PCR tests you more commonly find at a testing facility. According to the Centers for Disease Control and Prevention, PCR tests detect viral RNA and can take days for a positive or negative result, whereas the antigen test detects certain proteins in the virus and can take less than 30 minutes for a result.

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"In the symptomatic people, so if you have a fever, chills, a cough, something like that, they're around 90% as sensitive at picking up the disease as a PCR test," said Baird. "The real problem is with the asymptomatic individuals."

Because the tests are less sensitive without symptoms, the issue is for those that are asymptomatic that are using the tests to screen for the virus before attending an event. He said the best use-case scenario is to take the test if you are already feeling sick. 

Those who question the efficacy of the rapid tests and want to follow up with a PCR test shouldn't do so, at least not right now, Baird said.

"For right now, if you're feeling ill and you do an antigen test and it's positive, you should consider that to be a positive. A real positive," said Baird.

Baird said once transmission rates lower and you feel symptoms but a rapid test comes back negative, then it may make sense to follow up with a PCR test.

"After the surge is over here in the next few weeks, once things (cases) are not so common, you may want to then, if you really don't think that it makes much sense you haven't been exposed, you might want to confirm with a PCR test," said Baird.

The website, COVIDTests.gov, features a link for Americans to order up to four at-home tests per residential address, to be delivered by the U.S. Postal Service.

RELATED: How you can order 4 free COVID tests from the government

The federal government is limiting the number of tests any household can order due to projected high demand. Four tests can be shipped per household, not per person.

The White House said when announcing this plan that more tests could go out at some point to each household, but that depends on supply.

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