What Causes a False-Positive Rapid COVID Test?

For the most part, you can rely on at-home rapid COVID-19 tests to let you know if you’ve got the virus. That said, rapid COVID tests can be wrong. If you get a false-positive COVID test, it could make you think you're infected when you're not.

However, false-positive COVID test results don’t happen often, according to William Petri, Jr., MD, an infectious disease physician with UVA Health, told Verywell.

If you have COVID-like symptoms and test positive, you're very likely infected. If you're asymptomatic, but have a positive rapid test, it's still likely that you have the virus, said Thomas Russo, MD, a professor and chief of infectious disease at the University at Buffalo in New York.

Under what circumstances would you have a false-positive COVID test result then?

You Have Some Leftover Virus

At-home rapid antigen tests use antibodies to detect proteins in the virus that causes COVID-19.

Home tests usually target a protein called the nucleocapsid protein (N protein) or the spike protein, which can latch onto cells. Many at-home tests target several proteins at once.

It’s possible that a home COVID test could pick up antigens from a previous infection, William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, told Verywell.

“Sometimes, tests can remain positive for some period of time after you have recovered,” said Schaffner, adding that the test can “detect dead virus that is no longer infectious.”

Petri explained that a test “just detects fragments of the virus.”

Those lingering positive tests are one reason the Centers for Disease Control and Prevention (CDC) does not recommend testing out of COVID isolation. Instead, whether you can end isolation after day five depends on your symptoms.

“Home tests can be persistently positive for an indeterminate period of time. It’s a bit uncertain of the reliability to use the tests to give you an all-clear,” Schaffner said.

You Made a Mistake While Taking the Test

You have to get your own sample, usually a nasal swab or spit, for an at-home test. Then, you have to mix your sample with a solution that comes with the test kit. Russo said that user errors, like not getting a good nasal swab or not mixing the solution correctly, can lead to inaccurate test results.

However, Russo said it’s “much more likely you’d get a false negative than a false positive” if you make these mistakes.

Even if you’ve done many COVID tests by now, it never hurts to read the instructions—especially if you’re using a new kit or haven’t taken a test in a while.

It’s also important to make sure that you never re-use a swab to get your sample or share a swab with someone else.

Your Test Was Expired

It’s possible—but unlikely—that an expired test could lead to a false positive. “I would guess it’s more likely to result in a false negative because the reagents lose reactivity,” Russo said.

COVID tests do have expiration dates, but the Food and Drug Administration (FDA) has extended many of them. The date stamped on the box your test came in may not reflect the actual expiration date. There should be a sticker or another marker on the box that shows the updated expiration date.

The FDA has a list of authorized rapid COVID tests. Check to make sure that the test you have is not on the recalled or counterfeit list.

You Spilled Soda on Your Test

Research published in the International Journal of Infectious Diseases in 2021 showed that sodas, energy drinks, alcoholic drinks (including vodka, whiskey, and brandy), commercially bottled mineral water, and carbonated mineral water caused a red test line to appear on home COVID-19 tests. However, the study also found that when equal volumes of the solution and the beverage were mixed, no false-positive results occurred.

It’s unlikely that you would accidentally spill soda or another drink on your COVID test. But if you do, Russo suggests just using a fresh test kit.

What to Do If You Think You Got a False Positive

Experts stress that false-positive at-home COVID test results are uncommon. As Russo said, false-positive results are especially unlikely if you have symptoms.

“If you test positive and have symptoms of COVID-19, it’s very likely that you have COVID-19,” said Russo.

If you get a positive result on a rapid COVID test and feel that it’s incorrect, Schaffner recommends testing yourself again with a different test. Another option is to call your healthcare provider and ask for a PCR test—the gold standard of COVID-19 testing.