dream club Can I Use an Expired Covid Test?

As the government ships out another round of free Covid tests, some appear to have arrived already expired.

That doesn’t mean you can’t use them: The Food and Drug Administration has extended the expiration dates for many tests after collecting additional data from manufacturers showing their tests remain effective.

“It’s important to understand that you can rely on these Covid tests to be accurate,” said Courtney Lias, the director of the office that reviews in vitro diagnostics at the F.D.A.

How does the F.D.A. confirm tests still work?

Testing kit manufacturers were eager to get on the market as soon as possible at the height of the pandemic, so they submitted their products to the F.D.A. with expiration dates that were only around six months later. But in the years since, manufacturers have conducted additional assessments to confirm the tests work for a longer period of time. The F.D.A. has approved extensions for these tests on a rolling basis, sometimes as long as a year or two past the initially listed expiration date.

To get an expiration date extended, “these companies are required to literally take their product and stick it on a shelf and wait,” said Nathaniel Hafer, an associate professor of molecular medicine at the UMass Chan Medical School.

For example, Acon Labs, which makes Flowflex at-home tests, assessed batches of old tests every three months to ensure they still worked, said Michael Lynch, a vice president of sales and marketing at the company. Acon Labs added inactive virus particles to mucus from volunteers and used those samples to confirm the tests continued to produce accurate results.

You can check whether your test is truly expired by looking at the lot number and checking it against this F.D.A. list.

The F.D.A. also makes sure that Covid tests work against the variants that are currently circulating. Tests stay effective because they pick up on part of the virus that has not changed, even as new variants have evolved, said Dr. Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco. The F.D.A. has estimated that at-home tests will detect the virus at least 80 percent of the time when someone is infected.

What if my test really is expired?

Both the liquid that comes in the dropper with Covid tests and the test strips themselves can degrade over time, said Dr. Chin-Hong. That means that if your test’s expiration date has not been extended, you should not use it past that point — otherwise, you risk getting a false result.

Tests can also be damaged if they are exposed to extreme heat.

“If you’re having it in direct sunlight on the dashboard of your car for months or weeks, I probably wouldn’t be comfortable with it regardless of what the expiration date is,” Dr. Chin-Hong said.

You should always make sure the control line — which typically appears next to the “C” — shows up when you use a rapid testdream club, to make sure it’s working.

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