How a COVID Home Test Works and When to Use One

More health experts recommend swabbing before socializing to slow the spread of the virus

Scott Olson / Getty Images

By:

Rachel Nania

En español

Published January 11, 2022

Health officials are increasingly emphasizing the importance of rapid at-home testing as a way to help slow the spread of COVID-19, especially with the highly contagious omicron variant driving up new cases to record-breaking numbers.

These over-the-counter tests, which first showed up on drugstore shelves in the spring of 2021, require a quick swab of the nose and deliver results in about 15 minutes. And soon their price tag could drop from about $20 a box to zero, as the federal government moves to distribute some by mail and have private insurance companies reimburse the cost of purchased kits for people on their health plans.

How reliable are these tests? And when should you consider taking one? Top experts answer common questions and offer helpful tips for taking a COVID test at home.

How do rapid home tests work?

Similar to many COVID tests administered at doctor's offices and testing sites, an at-home version can determine whether you’re infected with the coronavirus by way of a sample swabbed from your nose. These tests, called antigen tests, work by looking for the presence of specific proteins associated with the coronavirus. If they are detected, a positive result appears on a test strip in a matter of minutes, much like a home pregnancy test.

“And that's helpful because that then allows you to make individualized decisions about how you keep yourself away from other folks, how you get your medical care and how you stop transmission cycles with your behavior,” Cameron Wolfe, M.D., an infectious disease specialist at Duke Health and an associate professor at the Duke University School of Medicine, explained in a recent briefing.

When should you take an at-home test?

Even if you’re fully vaccinated, it makes sense to pull out an at-home test if you’re having symptoms of COVID-19 or have been exposed to the illness, says the Centers for Disease Control and Prevention (CDC). It’s also recommended to self-swab before gathering indoors with others — whether that’s dinner with a small group of friends, a holiday get-together with family or a large event, such as a concert.

“The way that I would recommend using rapid antigen tests is really as a screening method,” Stephen Kissler, a research fellow in the Department of Immunology and Infectious Diseases at the Harvard T.H. Chan School of Public Health, told reporters on Dec. 7.

It can take days to get results back from the standard PCR tests (short for polymerase chain reaction) you get at many doctor's offices and testing sites. “And by the time you get the test back, oftentimes the result that it gives you is no longer very meaningful,” Kissler says, because it’s possible you got infected during the waiting window.

A rapid test done from the convenience of home, however, provides “immediate, actionable results,” says Gigi Gronvall, a senior scholar at the Johns Hopkins Center for Health Security and an associate professor at the Johns Hopkins Bloomberg School of Public Health. “If you test positive, don't be around other people, because you've got infectious virus in your nose. So it's a good public health tool for making sure that people who are potentially contagious stay to themselves.”

The key is taking the test as close to your plans as possible — aim for the same day, explained Matthew Binnicker, director of clinical virology at the Mayo Clinic, in a recent briefing. “That's going to give you the best information [on] whether someone has high amounts of the virus in their system at that time.”

The types of COVID tests

PCR test: A type of molecular test that looks for an active coronavirus infection by detecting genetic material from the virus. A sample is usually obtained by a nose swab, although a throat swab or saliva sample will also do the trick. You can get these tests at a doctor's office or testing site. Because these tests are analyzed in a laboratory, it can take a day or more to get results back. These tests are considered the most accurate available.

Rapid test: Also known as an antigen test, this type of test looks for pieces of protein from the coronavirus, usually by way of a nasal swab. Rapid tests — which can be administered in a doctor's office, a pharmacy or at home — deliver results much faster (about 15 minutes) than PCR tests, since they don’t need to be analyzed at a laboratory. The tests are considered accurate when there is a large amount of virus in the body but may miss an early infection.

Antibody test: This type of test can help determine if you’ve already had COVID-19; it does not identify a current infection. Using a blood sample, the test looks for antibodies produced by your immune system to fight off an infection. Fully vaccinated? Just know that COVID-19 vaccination may cause a positive result for some but not all antibody tests, the FDA says.

Source: Yale Medicine/FDA

Which home test is best?

The Food and Drug Administration (FDA) has authorized several over-the-counter home testing kits, and a handful are already available at pharmacies and major retailers, although surging demand may make them difficult to track down in some areas.

That’s why the best test is really “the one you can find on the shelves at your local store,” Kissler says, adding that most of the tests “have pretty comparable sensitivity and specificity for detecting SARS-CoV-2,” which is the official name of the virus that causes COVID-19.

If you are purchasing your test online from an unfamiliar retailer, be sure to confirm that the product has emergency use authorization from the FDA, since the agency has seen fraudulent test kits being sold on the internet. This should be clearly marked on the box. You can also double-check the FDA’s website for a list of authorized COVID tests.

Another tip: Check the label for how long the results take; that could make or break your decision to go with one brand over another.

“I tend to like the tests that give me the results sooner, because oftentimes if I'm using a rapid test, it's because I'm on my way somewhere and I want to know whether or not I've got the virus,” Kissler says. “So a test that gives me a return in 10 or 15 minutes is a little bit more convenient for me than a test that takes an hour.”

Ease of use is another factor to consider when selecting a test. Some kits require weaving a long swab through a card-shaped reader; others call for dunking a test strip in a vial of solution. “It's sort of a matter of personal preference,” Kissler notes.

Tips for taking a COVID test at home

Make sure the test you purchased has emergency use authorization from the FDA. This should be clearly marked on the box.
Check the expiration date, also printed on the box, and make sure the test has not expired.
Wash your hands and make sure you have a clean surface on which to perform the test.
Follow the instructions provided by the manufacturer. Johns Hopkins’ Gigi Gronvall also suggests looking to see if the test maker has a demonstration video online, which can help you become familiar with the process.
If your self-test is positive, tell a health care provider, who can help you determine next steps. You should also stay home and away from other people.
If your test kit recommends serial testing, follow instructions for when to perform the second test.

Source: CDC

How accurate are COVID home test results?

It’s true that PCR tests are more sensitive than antigen tests, meaning you’re less likely to receive a false negative if you go that route. But antigen tests “are very accurate when you are most infectious,” Gronvall says. “They're actually equivalent to PCR for that time period when you are most dangerous to others.” A recent study led by researchers at the Johns Hopkins University School of Medicine found that the coronavirus was accurately detected by rapid antigen tests in 87 percent of hospital patients with symptomatic COVID-19 and 71 percent with asymptomatic cases of the illness. When it comes to omicron, the FDA issued a statement in late December that said antigen tests do detect the new variant, “but may have reduced sensitivity.”

False positives are rare with rapid antigen tests, Gronvall adds. So if you test positive with an at-home test, you likely have COVID and should isolate yourself from others. You can always confirm the diagnosis with a follow-up PCR test or another antigen test, since "the accuracy of your result goes up with multiple tests,” Gronvall explains.

If the results are negative, it means the test didn’t detect the virus, but it doesn’t rule out infection completely, the CDC says. It could be that your infection is in the early stages and you don’t have enough virus in your sample for the test to turn positive. Repeating the test at least 24 hours later will paint a clearer picture. Some home kits come with two tests for this very reason.

“Of course, [home tests] don't bring the risk of bringing infection to a gathering down to zero, but they do reduce the odds by an awful lot,” Kissler says. And remember: A negative test is just a snapshot of your status at that moment in time. “[It] really doesn't clear you for very long — basically just that day and maybe the next day,” he adds.

What else should I keep in mind?

Testing, whether it’s done at home or in a health clinic, isn’t a substitute for other prevention measures, like vaccines, masks and physical distance. It’s just another risk-reduction strategy that can help keep people, especially high-risk individuals, safe while the virus continues to circulate at high levels.

Kissler is hopeful there will be at-home testing options for respiratory illnesses beyond COVID, such as flu. They could go a “long way” toward keeping schools and workplaces running smoothly, he says. But in the meantime, all eyes are on the ability for fast and convenient testing to curb winter surges by stopping the spread of COVID, especially as people get together in person.

“We know that super-spreader events, where a single infection infects many others, really drives the spread of this virus hugely. And rapid antigen tests can really reduce the odds of something like that happening,” Kissler says.

At-Home Tests for Travelers

by Bill Fink

You can use a rapid antigen test to regain entry into the U.S. after traveling abroad, but you’ll need to do your homework. Not every COVID test sold over the counter is accepted under the federal government’s order. For starters, the tests approved for international travel must “include a telehealth service affiliated with the manufacturer of the test that provides real-time supervision remotely through an audio and video connection,” according to the CDC. This means you’ll need a good WiFi connection so a designated medical professional can watch you administer the test and observe the results.

Self-tests deemed acceptable for international travel also must be able to produce approved documentation to share with airline and customs officials and they must be authorized by the FDA or the relevant national authority where you’re taking the test. The good news is that several companies have released FDA-authorized self-tests that meet the CDC’s re-entry requirements, including Abbott’s BinaxNOW home test with telehealth service ($70 for a two-pack) and Qured’s Quidel QuickVue video supervised rapid test ($45).

Traveling without a test? Check with your hotel about options. Many international hotels offer approved and supervised tests for their guests free of charge — it’s almost becoming a standard part of the check-out process. Local clinics and some airports offer CDC- and airline-approved tests as well, although costs and availability vary widely. Whatever your testing plan, make sure to check the latest CDC travel and testing requirements before your trip — you don’t want to be denied access to your return flight with an unapproved test.