Can we trust rapid COVID-19 tests? Mayo doctor weighs in

Dr. Matthew Binnicker, Director of Clinical Virology at Mayo Clinic, answers some of our questions about COVID-19 testing:

FOX 9: Can we trust the results of rapid tests?

Dr. Matthew Binnicker: I think the reliability depends – one, on the test, and two, on the circumstance.

Not all rapid, antigen, at-home tests are created equally, so I definitely encourage individuals to get out on the FDA website and make sure any test they pick up has received emergency authorization to be used during the pandemic.

Then in terms of scenarios where they’re most reliable, if you have symptoms, respiratory symptoms like a sore throat, cough, fever, and you test positive for COVID-19 by one of those at home antigen tests, that result is reliable. That likely means you have COVID-19.

If you don’t have any symptoms of COVID-19 and you just want to determine whether you’re infected before you go and meet with family members or work get together, if you test positive, that could be a false positive. The specificity of those at home tests is not quite as good in people who lack symptoms, so it’s still good to get a lab-based PCR test.

FOX 9: We’ve been seeing these videos and kind of things swirling around on social media about people testing their throat with a swab. What do you think of that? 

MB: Yeah, a lot of discussion on social media about this, likely coming from the fact that patients who infected with omicron may experience a sore throat - that’s one of the common early symptoms, and there have been some anecdotal reports by patients that test a throat swab and getting a positive result.

What we’re recommending though, at least what I’m recommending, is you stick with the instructions of the test you’re using most of the at-home antigen tests were only studied in nasal swabs. The companies that make these tests didn’t specifically look at how the test preformed using other types of swabs like a throat swab.

Until we get more evidence and data showing that the tests should be done on a throat swab, stick with the recommendations of the manufacturer of that test and follow the instructions.

FOX 9: What are your thoughts on when someone does have COVID-19 testing their way out of it or staying isolated until they have a negative test? 

MB: The CDC has just updated some of their isolation guidelines. They updated their guidelines to state that if you're test positive they would like you to stay in isolation for a period of five days and then when you come out of isolation you need to wear a mask for the next five days, so a total of ten days.

I think it’s not a bad idea after that five-day isolation period to take an at-home antigen test. If you test negative, probably a good indicator that you’re not shedding high amounts of the virus still. I’d still recommend following the CDC’s recommendation of wearing a mask for the next five days.

PCR testing probably not going to be needed after that period of isolation because we know that the PCR test can stay positive several weeks after a person is initially diagnosed.

FOX 9: What if you are experiencing symptoms, you test negative on a rapid test and you’re waiting for the results of a PCR test?

MB: If you have symptoms, you use an at-home test that comes home negative and those symptoms persist or get worst, it’s definitely a good idea to get a lab-based PCR and you should stay home and isolate until you get the results back of that lab-based PCR because the antigen test might have missed an early infection.

FOX 9: If you learn that you have come in contact with someone who has COVID-19 and you want to get a PCR test or you have symptoms popping up when should you do that?

MB: If you’re exposed to someone who has as documented case of COVID-19, if you go get tested that day or the next day, not enough time has gone by for the virus to incubate and get to the levels that’s going to be picked up by a test.

We’re recommending if you have an exposure you need to wait about 72 hours so three, maybe four, days after the exposure to get tested.

Now, if you have symptoms it’s a different story. Once you start developing symptoms you’re probably going to have higher amounts of the virus so going and getting tested as soon as those symptoms start to develop is a good idea.

FOX 9: Say you’re fully vaccinated, and you learn that you’ve been exposed to someone who has COVID-19, but you’re not experiencing symptoms. Should you be isolating?

MB: Current recommendations are if you’re fully vaccinated and not yet eligible for a booster or have been boosted there are more, I would say, lenient guidelines for those individuals and so you don’t need to isolate if you’re fully vaccinated and boosted.