Rapid COVID tests are convenient and easy to use because you can take them at home. But it's important to know how to interpret their results, when you should take another rapid test and when you should really opt for a PCR test instead.
The gold standard for COVID-19 testing is still the PCR test, which relies on polymerase chain reaction technology to amplify and detect even tiny bits of viral DNA that may be present in your sample. But it can take hours to days to get your results, and depending on availability in your area, it may be challenging to get a PCR test when you need it most.
At-home antigen tests, which use a different type of technology to find proteins on the surface of the virus and return results within minutes, solve many of those issues. But the trade-off is that their results aren't as reliable as those from a PCR test — especially if you don't have COVID-19 symptoms.
In fact, a new study published in JAMA Network Open Wednesday, for which 723 college students self-administered Abbott's BinaxNOW rapid antigen test, concluded that the product's "use as a screening tool for asymptomatic infection is ... limited" with the omicron variant. Of the students, 46 tested positive with the rapid antigen test, 35 of whom were symptomatic. Twenty people tested negative with a rapid antigen but positive on a PCR. The test was determined to have a sensitivity of 63%, detecting 46 of 73 total COVID cases.
In a statement about the study, Abott told TODAY: "Rapid antigen tests are an indispensable tool in slowing the spread of COVID because they detect people who are infectious and therefore most likely to spread the virus to others. Abbott’s research, as well as third-party research, continue to demonstrate BinaxNOW’s ability to detect people with COVID, including Omicron, when they are infectious and likely to spread the virus. The test shows performance of 95.6% positive agreement (sensitivity) in people seven days or less post-symptom onset with high viral loads."
"The rapid at-home tests are fine tests. They're not bad tests," Dr. Emily Volk, president of the College of American Pathologists, told TODAY. "But they're not as sensitive, and they're not as specific as the PCR test for COVID-19 that you can't do at home."
When should you test for COVID-19?
As soon as you develop any symptoms of COVID-19, do not hesitate to take a test, Omai Garner, associate clinical professor and director of clinical microbiology at UCLA Health, told TODAY. In people who have symptoms, the rapid antigen tests have "good positive, predictive value," he said, meaning that you can generally trust a positive result under those circumstances.
The Centers for Disease Control and Prevention also suggest getting tested in these scenarios:
- You've been exposed to someone with COVID-19
- Before and after you travel
- Screening before an event
Also, if you've had a COVID-19 infection and are wondering if it's OK for you to leave isolation, you can take a rapid test to help figure out whether you're still contagious.
And, yes, rapid tests still generally work for the omicron variant, Dr. Amy Mathers, associate professor of medicine and pathology and associate director of clinical microbiology at the University of Virginia School of Medicine, told TODAY. But with so many different tests on the market, it’s hard to make blanket statements about their efficacy, and recent research shows some work better than others.
It's still too early to know how rapid antigen tests perform against BA.2 and other subvariants, Mathers said. "They all have slightly different chemistry and they're all proprietary," she explained. "So they may or may not be affected by different variants differently."
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If you have symptoms but your rapid test is negative...
As mentioned above, if you have symptoms and test positive on an at-home test, you should assume those results are generally correct and take the appropriate steps to isolate.
"The problem is: If it's negative, it doesn't mean the person doesn't have COVID," Garner said. "They just may not have a high enough amount of virus to turn a rapid test positive."
With the omicron variant (and its subvariants), it generally takes about three days from exposure to start feeling symptoms, he added. And keep in mind that symptoms can include obvious things, like fever, as well as things like a runny nose and fatigue that can be confused for allergies or a cold.
So if you have any of these symptoms but test negative, Garner recommended taking another rapid test 48 to 72 hours later. At that point, if you do have COVID-19, you have a better chance of testing positive because you'll have a larger amount of the virus in your system. If the result of that test is also negative, you can be more confident that you don't actually have COVID-19.
Despite their advantages, the rapid tests "come with a lot of caveats around not being as sensitive early in infection, even if you're infectious," Mathers said. "So repeating a test is a way to kind of compensate for the lack of sensitivity."
During those few days when you don't yet have the result of your second test, all the experts recommended taking as many precautions as you can, meaning you should limit your interactions with other people and wear a mask if you must come in contact with others. "In that space — and this has been a little bit lost — that person can still be contagious," Garner said. So it's important to still be careful when you're in that testing limbo.
Another option is to take a PCR test at any point for more sensitive and specific results, Volk said. Mathers agreed: "If you were exposed, you're having symptoms and you initially test negative, you probably want to repeat that test again the next day or just go ahead and get a PCR test."
Keep in mind that people who are up to date on their vaccinations may find that it takes a bit longer to get a positive result on a rapid test than those who are unvaccinated, Garner said. "On day one of symptoms, or even 24 hours before that, (unvaccinated) people can have very high virus totals and would test positive on a rapid test," he explained. Whereas, if you are fully vaccinated, you might experience a "delay in rapid test positivity."
Mathers said there isn't any conclusive research on that potential timing difference yet, but there is a theoretical basis behind it: In one study looking at people infected with alpha and delta coronavirus strains, researchers found that vaccinated people had lower amounts of the virus. "We don't have any robust data showing how that affects the antigen test performance, but one could speculate that it might decrease the sensitivity," she explained.
Regardless of your vaccination status, Volk recommended "testing daily until you feel confident you don't have COVID," provided you have enough rapid tests on hand to do so. Or, if you're able to access a PCR test, skip the rapid tests entirely and go for that instead.
Related: How to properly store your at-home COVID-19 rapid tests
If you don't have symptoms but may have been exposed to COVID-19...
Say you were at a dinner party, the gym or working in the office with someone who ended up testing positive a day later. Even if you don't have symptoms, those are situations in which you should take a test a few days after the exposure and quarantine yourself until you're in the clear, according to the CDC’s guidelines.
But if your rapid test result is negative, should you trust that result? Rapid antigen tests are generally less accurate when detecting COVID-19 cases in people who don’t have symptoms, so this is where it gets tricky.
The experts told TODAY that, if there's any way to do so, you should really opt for a PCR test in this scenario instead of a rapid test.
"If you are asymptomatic and you've been exposed and you want to see if you're turning positive or not, I would recommend using a PCR methodology simply because it's going to be more specific and more sensitive," Volk said. "It's just going to work a little bit better."
That doesn't mean the rapid tests are useless. It just means that, if you have the option to get a PCR under these circumstances, you should go with that.
If truly all you have access to is rapid tests, they can still be helpful. But you should then rely even more on other precautions, like wearing a high-quality mask or holding your gathering outside, to further reduce the risk of spread, Mathers said, especially if you're spending time with people at high risk for severe COVID-19.
That said, there are situations where it makes sense to use rapid tests in people who don't have symptoms. One of those is screening at a large event, Volk said, like a conference, concert or sports game. When you need results quickly at a large scale, that's where rapid tests come in really handy.
We also have more data to support the use of rapid tests in people without symptoms when they're coming out of a COVID-19 infection — to determine whether they're still contagious — rather than in diagnosing a new infection, Garner said.
"I just know it must be frustrating and confusing," Mathers said of the rapid antigen testing situation. But it's crucial to remember that testing is just one of many tools we have now to reduce the spread of COVID-19, and they work best when we use them all together.