How Accurate Are At-Home Covid Tests? Here’s a Quick Guide

In the beginning months of the pandemic and for a coronavirus test, you had to visit a health center, a laboratory or a specific testing site. It was often difficult to get the results, and it took up to a week to get them.

Americans can now conduct rapid antigen testing from the comfort of home. Many of these tests can be performed without the need for a prescription and results are returned in as little as 15 minutes.

The demand for the tests has increased as the highly infectious Delta variant spread, and schools and offices reopened. Now the more dangerous Omicron variant is available. “All the manufacturers are ramping up production, but right now they can be hard to find,” said Gigi Gronvall, a testing expert at Johns Hopkins University.

Experts agree that rapid antigen tests are not without their limitations. However, they can be a valuable tool for public health, especially if you know how they work.

“Having that information and being able to make better decisions is very powerful,” said Mara Aspinall, an expert in biomedical diagnostics at Arizona State University who is also on the board of directors of OraSure, which makes rapid Covid tests. “And the ability to do this on a while-you-wait basis is something that we couldn’t do a year ago.”

What tests are available to you?

Several rapid antigen tests, including the Abbott BinaxNOW (Ellume Covid-19 Home Test), the Quidel Quidel QuickVue Home Covid-19 Test, and the Quidel BinaxNOW (Abbot BinaxNOW), are available without the need for a prescription. Prices start at $7 per test, but President Biden has announced plans for a reduction of around one-third.

All three can detect small viral proteins called antigens. To perform the tests, you need to place a small nasal swab into your nostrils. Next, expose the swab with a few drops chemicals. They give results in approximately 15 minutes.

Although the tests are simple, each one requires a slightly different process that should be followed. “If you’re doing at-home tests, you must read the instructions and follow them meticulously,” said Dr. Patrick Godbey, Former president of the College of American Pathologists.

Ms. Aspinall agreed. “This is not the time for creativity,” she said.

What accuracy are rapid antigen testing?

Polymerase chain reaction tests, which have typically been considered the gold standard for detecting the virus, are typically performed in a laboratory and involve making many copies of the virus’s genetic material. This process aids P.C.R. P.C.R. can detect even the smallest trace of the virus.

Rapid antigen tests that do not amplify the virus are less sensitive to P.C.R. tests. The test may return a false positive if it is taken in the early stages of an infection.

Some of the at home rapid antigen tests Their overall sensitivity is approximately 85 percent. This means that they catch roughly 85 percent of those who are infected and miss 15 percent. Some studies have shown that their real-world performance is even lower.

Studies have shown that the tests are sensitiver in patients with symptoms than those without them and are most sensitive during their first week.

And antigen tests are excellent at flagging people who have high viral loads — and who are thus most likely to be actively transmitting the virus to others, experts said.

“The more virus you have in your nose, the more virus you’re breathing out into the air, and the more virus other people can then breathe in,” Dr. Gronvall said. “The tests are very accurate, and correlate very well with P.C.R., when people are most infectious.”

Using the tests repeatedly — to routinely screen students for the virus, for instance — can compensate for their lower sensitivity. Researchers discovered that rapid antigen testing was able to identify 98 percent, in line with P.C.R., when they tested infected college students as well as employees, in a recent study. tests.

How and when should I use them?

Experts say that rapid at-home antigen testing is a good option for those who have been exposed to the disease, who want to determine if a sore throat has Covid-19 or just a common cold.

Experts said that anyone with symptoms should take a rapid test for antigen immediately. However, people who have had an exposure to the virus in the past should wait three to five business days before taking a test. Tests too soon, before the virus can replicate, increase the chances of false negatives.

“And that is a critical, critical piece,” Ms. Aspinall said. “There are a lot of people taking a plane, getting off the plane and saying, ‘I’m negative — I can go visit Grandma.’”

At-home testing results may not be accepted by some businesses, travel agencies, and other organizations if there is no proof of negative results.

I tested negative. Now what?

The best rapid antigen tests are those that are repeated. If you test negative for the virus after possible or known exposure, Experts suggest that you have a second test within a few days of developing symptoms of Covid-19.

“Tests are a moment in time,” Dr. Gronvall said. “You don’t know the day or the hour” that the virus “breached your immune defenses and took up residence.”

She noted that it might be difficult to convince people to use the tests often if they are not more affordable and readily available. “We definitely need more tests on the market, and we need them to be lower cost,” Dr. Gronvall said.

I was positive. Now what?

Rapid antigen testing is highly specific, so they are prone to false positives. A positive result can be more likely to be false positive if the virus prevalence is low. In these cases, people might want to take another test. (The Centers for Disease Control and Prevention recommends laboratory based molecular testing, such as a P.C.R. For confirmatory testing, use the test.

Experts recommend that you not wait for the results of the second test to take precautions. If you are positive for the disease, you should immediately isolate yourself and monitor your symptoms. You can also seek medical attention if necessary.

Consumers are encouraged to report any positive results to their local health authorities.

“If we don’t report tests accurately, we still won’t have a good idea of the actual caseload — how many people are running around that might be contagious, that might be passing this along to other folks,” Dr. Godbey said.