COVID Tests: From Rapid Home Tests to PCRs, Here's What to Know Right Now

Updated Wednesday, Jan. 19.

In an ideal world, the U.S. would be awash in COVID tests. Anyone exposed to the coronavirus could self-test or go to a lab or clinic if necessary.

But right now, self-tests are in short supply in many parts of the country.

Test manufacturers are ramping up production, so hopefully — at some point — you won’t be seeing those “no tests available” signs at your local pharmacy or have to wait a week or more for tests ordered online.

What’s more, the Centers for Disease Control and Prevention has changed its testing guidelines in the wake of the omicron surge in the U.S. — and public health researchers are critical of some of the recommendations.

The result is a lot of confusion, so we’ve compiled some frequently asked questions about COVID-19 tests. Don’t have time to go through the whole guide? Click the links below to skip to a specific section:

• What types of COVID tests are there?
• What’s the difference between antigen and PCR tests?
• When is the right time to get tested?
• How many tests should I take?
• Should I get tested before seeing people?
• If I test negative, how accurate is that result?
• What happens if I test positive?
• Do the tests detect omicron?

What types of COVID tests are there?

There’s the rapid, do-it-yourself home test, which involves swabbing your nose and takes about 15 minutes to display a result on a test strip provided in the kit. These cost about $20 for a package of two tests. They’re known as antigen tests — antigens are basically the proteins from the virus that the rapid tests can identify.

Then there’s the PCR test performed in a lab or clinic. PCR stands for polymerase chain reaction, which is a technique for amplifying trace amounts of virus DNA. Depending on how busy your local technicians are, you may have PCR results within a day, or it may take several days. A PCR test usually costs about $150 without insurance.

There’s a third type of test: a blood test that looks for antibodies after you’ve been sick, and some samples can even be taken from a finger prick at home and sent to a lab. But they are not used to diagnose COVID-19.

The cost to diagnose COVID-19 is an eligible medical expense for tax purposes, which means you can use your health flexible spending account (health FSA), health savings account (HSA), health reimbursement arrangement (HRA) or Archer medical savings account (Archer MSA) to pay for or get reimbursed for an at-home COVID test kit.

Most insurance policies cover PCR and rapid tests administered by health providers. As of Jan. 15, people with private health insurance can get reimbursed by their insurer for the cost of up to eight at-home COVID tests per month. Read more about getting reimbursed for at-home COVID tests through your health insurer.

You also now can order free at-home COVID-19 tests online from the federal government and the United States Postal Service. The White House program, which went live Jan. 18, offers four at-home COVID tests to every household in the United States, to be shipped by USPS.

The tests and shipping are completely free of charge. Read more about how to order free tests through USPS.

What’s the difference between antigen and PCR tests?

The PCR test is much more accurate at identifying an infection because it can amplify traces of the virus — in other words, even if you have a small amount of virus, it can detect it. So it can tell whether you’re infected even a day or so after you develop what appear to be COVID-19 symptoms or a few days after exposure to someone with COVID-19.

The antigen tests don’t magnify the amount of virus in the sample you take, so you need a pretty high viral load to test positive. As Susan Butler-Wu, associate professor of clinical pathology at the Keck School of Medicine of the University of Southern California, puts it: “It’s a test for [determining whether you have] a lot of virus.”

So you might test negative on a home test even if you are infected — at the beginning or the end of your illness, for example, when you don’t have a lot of virus.

The more urgent question, says Butler-Wu, is: “Which test can you get?”

If you have symptoms and likely have been exposed to the virus by traveling or socializing, a positive antigen test is probably enough evidence that you have the virus, says Dr. Abraar Karan, an infectious disease physician at Stanford University.

As for PCR tests, availability depends on the demand in your community. Some testing facilities are slammed, with few appointments available and hours-long waits even if you can snag an appointment. And it can take several days to get results from a PCR test.

When should I test?

The answer depends on whether you can get a test — and what you’re using it for. A test can be used to tell you whether you have COVID-19 — for instance, if you have symptoms or you’ve been around someone who tested positive. And they also can be used as an added precaution before socializing (which we’ll discuss a couple of questions down).

If you’ve been exposed to someone with COVID-19, you should self-test. But not right away.

“If you’ve been exposed, wait a few days because testing right away could be negative,” Karan says. After you wait, “then we’ll be able to detect virus.”

The Centers for Disease Control and Prevention recommends self-testing either when symptoms develop or, if you aren’t showing symptoms, five to seven days after exposure. That would give enough time for the body to develop a viral load that can be detected by a home test.

With the omicron variant, there have been reports that rapid tests are negative during the first day or two of symptoms. So even if you’re showing symptoms, you might want to wait a day or two to take the first test, especially if you have a limited supply of tests.

How many tests should I take?

At least two.

Why test twice? Home tests are most accurate when you use them serially — at least two over the course of a few days. And if you have a limited supply of home tests, you will want to aim for the time when you are most likely to get an accurate result — say, on Day 5 and Day 7 after exposure.

“These tests absolutely have to be used serially, to be perfectly honest. They don’t have the sensitivity to be used one-and-done if they’re negative,” Butler-Wu says. “By repeating it, you’re allowing the virus to potentially grow more to the point, essentially, where now you can detect it.”

“If that test is negative, all that’s telling you is: At this point in time, you don’t have a ton of virus in you,” Karan says.

Should I get tested before seeing people?

“If you’re going to visit Grandma or something, yeah, I would probably rapid-test before that,” Karan says. “Or if I’m going somewhere where there’s going be a lot of people. If I’m contagious that day [and don’t know it], I could infect tons of people.”

A positive test result will tell you to cancel your plans and stay home and isolate.

But negative results don’t mean it’s time to rip the mask off in social settings. Rapid tests could be negative before a party and positive during it, just a few hours later — even if you’re vaccinated and boosted.

“To say that the negative test means being indoors unmasked — I think that needs to get rethought, pronto,” Butler-Wu says.

“Omicron has changed the game completely,” she says. “We know from Christmas soirees that occurred in European places that those exact scenarios happened: vaccinated people, negative tests and there was still spread.”

If I test negative, how accurate is that result?

There can be false negatives, especially soon after exposure when not much virus is present in your body, or if the virus is replicating somewhere other than where you were swabbed — for instance, in your throat instead of your nose.

However, that doesn’t mean you should use an at-home test to swab in other places that aren’t your nose. A recent viral TikTok video encourages viewers to swab their throats instead, but emergency physician Mary Mercer says that is not necessary. She’s part of the COVID-19 task force with the San Francisco Department of Public Health.

“You need to follow the directions for whichever at-home test you have,” she says. “You do not need to swab your throat in addition to your nose if it’s a nasal test.”

But if you tested negative and feel the result isn’t accurate, it may be a good idea to test again.

According to a pre-omicron study, the Abbott BinaxNOW antigen test was 92.6% accurate at detecting the virus in symptomatic people and 78.6% accurate in asymptomatic people, compared to PCR results in cases where people had viable virus.

It is also possible to have a false negative from a PCR test.

“Any test is a snapshot of what’s happening in the part of your body that was sampled at that moment. That’s all it tells you,” Butler-Wu says.

PCR tests are more sensitive and can detect lower amounts of the virus in the body, she says. However, if you were just exposed and are in the very early stages of incubation, you probably haven’t reached what doctors call the “limit of detection.”

That’s why the CDC recommends that people get tested at least five days after a possible exposure, or when they start noticing symptoms.

What happens if I test positive?

When you test positive, you should isolate yourself for a minimum of five days and wear a mask for five days after that, according to the CDC. If you have rapid tests, you can use them after five days to see whether you’re still positive, which would mean you need to continue isolating.

If you tested at a clinic, they will report the results to the local public health department for you. But if you test positive on a home test, you’re not required to report that to the department of public health, says Mercer, the emergency physician from San Francisco.

“We do recommend that if you have a positive test, you call your provider, your personal physician or provider to let them know that you’re positive,” she says.

If you’re worried that you have a false positive, those are pretty rare on PCR tests and usually happen because of contaminated samples, research has found.

A false positive on an antigen test is possible but fairly unlikely if the test is taken correctly, says Butler-Wu, especially if you develop symptoms and you know you’ve been exposed to someone with COVID-19. And a lot of people are being exposed at this current time of great spread to the omicron and delta variants.

If “there’s a bunch of COVID and I’m symptomatic, it’s probably a true positive,” Butler-Wu says.

Do the tests detect omicron?

Rapid tests may not be as accurate for omicron, the U.S. Food and Drug Administration said in late December — but they haven’t released data yet on why they are less accurate and to what degree.

The FDA also has warned that three types of PCR tests may not detect omicron.

Because of these issues, if you’re testing at home after symptoms or an exposure to someone with COVID-19, the use of two tests spaced a few days apart is critical.

This post includes reporting from KQED’s Kevin Stark, Carlos Cabrera-Lomelí and Carly Severn.