Your Questions About Home COVID-19 Tests, Answered
Are rapid antigen tests accurate? Should you swab your throat? With omicron surging, we have expert answers to these questions and more.
The omicron variant is now widespread in the U.S., and with it has come a huge demand for COVID-19 tests. Home tests are appealing because they allow you to avoid going to a testing center (which may feature long lines or a crowded waiting room) and they produce results in minutes.
“There’s a tremendous amount of enthusiasm and desire for these tests,” says Larissa May, MD, a professor of emergency medicine at UC Davis in California. But questions abound about how accurate they are, and how and when they’re most useful.
What Kind of COVID-19 Tests Can I Take at Home?
Right now there are three kinds of at-home COVID-19 tests. The ones you’re probably most familiar with are rapid antigen tests, like BinaxNow, which you can pick up over the counter at a pharmacy or online (at least when supplies are available) and get results in under an hour.
There are also some options for at-home molecular tests (which are generally more accurate than antigen tests; see below for more information). PCR tests are available—LabCorp’s Pixel is an example—but they require mailing your sample to a lab and waiting for a result. Rapid at-home molecular tests are also available, from companies like Cue and Lucira, but they’re pricey and thus not widely accessible to most people.
How Do Home Antigen Tests Work?
Antigen tests detect proteins on the surface of the SARS-CoV-2 virus that provoke your immune system to respond. Because they react only to proteins actually contained in the test sample, they can return a false negative result when virus levels are low, as is generally the case, for example, when someone is infected but hasn’t yet started showing symptoms.
Are Home Antigen Tests Accurate?
Yes. “At-home antigen tests are quite accurate, especially if you have symptoms,” Hafer says.
Still, they have some limitations. Antigen tests are more likely to return a false negative if you’re infected but you don’t yet have symptoms. That’s because they might not be able to pick up the low viral load of an early or waning COVID-19 infection. But when you’re symptomatic, antigen tests may be a reasonable marker of whether someone is infectious, May says, at least at the time they take the test. Note, however, that groups such as the Infectious Diseases Society of America (IDSA) have so far held that neither rapid antigen tests nor molecular tests can be taken as definitive proof of a person’s infectiousness.
The likelihood of a false result on an antigen test also varies depending on the prevalence of COVID-19 in a community, a March 2021 Cochrane review found. When there’s little virus circulating in the area, a positive result on an antigen test is more likely to be a false positive, and you should confirm the result with a PCR test to avoid needlessly isolating yourself. However, when there’s a lot of COVID-19 circulating, as there is in most places in the U.S. right now, the researchers found that there’s a higher risk of a false negative result on an antigen test.
The different rapid antigen tests available have different levels of accuracy. The Medical Letter, a publication for physicians, offers this chart summarizing their accuracy (PDF) based on data from the test manufacturers. (The PPA, or positive percent agreement, and NPA, or negative percent agreement, indicate the rate at which the antigen test results agree with a positive and a negative PCR result.) Keep in mind, however, that some independent studies of test accuracy have found that the real-world accuracy may be lower than what manufacturers report in their data, at least when it comes to the ability of a test to return a true negative result in someone without symptoms.
How Much Do Home Antigen Tests Cost, and Where Can I Get Them?
Drugstores such as CVS, Walgreens, Walmart, and others sell antigen tests over the counter, generally both online and in stores. Prices for a package of two tests start around $20. Shortages are ongoing, so you may have to hunt around at chain and independent pharmacies to find the tests. Some cities and states are distributing free at-home antigen tests, so check to see what may be available near you.
The federal government announced in December that it would soon be launching a site that will allow people to request free tests. That site, COVIDTests.gov, will start accepting orders for free tests Jan. 19.
Starting Jan. 15, people with private insurance should also be able to get at-home antigen test kits from pharmacies and retail stores free of charge or at a discount. The federal government is incentivizing health plans and insurers to set up a network of retailers across the country where plan members can get tests with no up-front costs. You’ll need to check with your own plan for details on where such tests will be available.
If you go to a pharmacy or store that’s not in your insurer’s network for this program, you can purchase tests and be reimbursed by your insurance company by up to $12 per test. Be sure to keep your receipt for reimbursement.
How Do I Use a Home Antigen Test?
The exact directions will vary by brand, so make sure to read them carefully before you begin. The Centers for Disease Control and Prevention recommends that you disinfect the surface on which you’ll be placing the components and wash your hands. Lay out all the materials in the test kit before you start the procedure, as if you’re practicing the chef’s technique of “mise en place” but for an infectious disease diagnosis instead of cooking.
The tests involve swabbing the inside of your nose—and it’s crucial to do this part correctly, so that you gather a good sample. Directions generally say to:
• Insert the soft end of the swab no more than ¾ inch into your nose.
• Firmly and slowly swirl the swab in a circle around the inside wall of one nostril at least four or five times, for a total of 15 seconds. Repeat this process using the same swab in the other nostril.
You then put the swab containing your sample into contact with some component of the test, such as into a tube of liquid that you’ve unsealed or against a card containing a test strip. Once you’ve finished all the steps, you’ll need to wait for a result. Be careful about keeping track of the time, according to what the test’s directions indicate. The results won’t be valid until a certain amount of time, but they’ll also become invalid if you wait too long. CareStart and QuickVue’s tests, for example, should be read 10 minutes after completing the procedure, but they become invalid after 15 minutes.
Should I Swab My Throat, Too?
Some anecdotal advice has circulated that if you suspect a case of COVID-19 but get a negative result on an at-home antigen test, you should try the test again but this time swab your throat as well as the inside of your nose. The theory behind the advice goes like this: some preliminary evidence suggests that the omicron variant begins replicating fastest in the throat, rather than the nose as earlier variants did. That means you might have better luck getting a true positive result on a test earlier in the course of an infection by swabbing your throat rather than just your nose, because a nose swab might return a false negative result for longer.
In theory, at least, this practice would make sense—if we had the evidence to back it up, says Stephen Master, MD, president of the American Association for Clinical Chemistry (AACC) and the chief of the division of laboratory medicine at the Perelman School of Medicine at the University of Pennsylvania. But we don’t yet have studies that address the question of how well throat swabbing works with the antigen tests we have available in the U.S. right now, which were designed and authorized to use nasal swabbing.
“The concern is that until we actually do the experiment, we don’t know if going to those other sites, whether saliva or back of the throat, would result in having a greater risk of a false positive of a false negative,” Master says. Different biological fluids—saliva vs. the mucus in your nose, for example—can have different effects on the result of the test.
For now at least, the FDA has advised against using a throat swab with the rapid tests authorized in the U.S.
It’s an urgent question that scientists need to study quickly, Master says, because the omicron variant is spreading so rapidly. If swabbing the throat is a better strategy, he says, we need to know as soon as possible so that we can detect cases of omicron earlier.
In the meantime, if you do go ahead and try out the throat swab to compare with the result of a nose-only swab, use care. In the U.K., where tests that combine throat and nose swabs are already common, Public Health England advises that you swab the throat first, and then the nose. Here’s a video with step-by-step instructions.
If your nose-swab-only test comes back negative but your throat-swab test comes back positive, what should you do? “I would view that in the same way as I would view someone having symptoms and not being positive yet by a nasal swab,” Master says. Because the prevalence of omicron is so high right now, it’s wise to behave as if you’re likely infected, at least until you can double check with follow-up testing.
What Should I Do After a Positive or Negative Result?
If you test positive on an antigen test, given that there are high levels of virus circulating in most places in the U.S. right now, you can trust it even if you don’t have symptoms, so you should take the recommended isolation measures.
Guidance varies somewhat on how exactly to interpret a negative rapid antigen test result. If you test negative but have symptoms of COVID-19, it’s relatively simple: You should follow up with a PCR test to confirm, according to the CDC, the IDSA, and Wolters Kluwer UpToDate, a tool for doctors. Continue to isolate yourself as if you tested positive until you get the result.
If you test negative and don’t have symptoms, you can feel somewhat reassured that you’re less likely to be infectious at that moment in time, particularly if you’re vaccinated. (UpToDate and the CDC say people who are not fully vaccinated and have had a known or suspected COVID-19 exposure, no symptoms, and a negative rapid antigen test result should confirm with a PCR test or quarantine.) But it doesn’t necessarily mean that you aren’t carrying the virus and that you wouldn’t test positive if you repeated the test the next day.
“It doesn’t sort of give you a free pass to assume that there’s no way you could spread COVID,” Susan Butler-Wu, PhD, an associate professor of clinical pathology at the University of Southern California in Los Angeles, told the American Association for the Advancement of Science’s SciLine in an interview earlier this month. This helps to explain how people can contract COVID-19 at events such as concerts that require negative rapid tests right before entry.
Still, combined with other mitigation measures, such as masking and ventilation, getting a negative result on a rapid antigen test right before joining an event like a family gathering can help provide another layer of protection to attendees. You’ll want to take the test as close to the start of the event as possible—such as at the door. May says negative rapid antigen test results can also provide some added assurances in school settings where, again, other measures like masking and ventilation are also being used.
How Should Home Tests Be Stored?
Keeping tests at room temperature is fine. A study in the Journal of Clinical Virology found that storing kits above 86° F or below about 37° F decreased the accuracy of the tests, but most home environments are likely to be more temperate than either of those extremes. Note that test kits do have expiration dates, so make sure yours hasn’t expired before you use it.
—Additional reporting by Lauren F. Friedman