Can I use expired COVID-19 tests?

If you have stockpiled COVID-19 tests at home during the great Omicron shortage, you may want to do some research before using your diagnostics. Like food and medicine, COVID-19 tests are rapid, but figuring out when they go bad isn’t always as simple as looking at the box.

Here’s what you need to know about COVID-19 home test expiration dates.

When does my COVID-19 test expire?

According to the U.S. Food and Drug Administration (FDA), the components of COVID-19 test kits can deteriorate over time, potentially affecting diagnostic performance and accuracy. Figuring out exactly how long a product will last, however, takes time. For example, to know whether a test is performing well after two years, the manufacturer logically needs at least two years of data. Since rapid COVID-19 testing is a relatively new product, companies are collecting a lot of that data in real time, meaning their expiration dates can and do change.

The FDA sets the expiration dates conservatively and then adjusts them as needed. For starters, home COVID-19 tests are usually authorized with an expiration date of four to six months after they’re made, the FDA says. But the agency can extend that window if new research results become available. That dynamic system means that the date stamped on the box of your test may not be the current expiration date.

In January, the FDA extended the recommended shelf life of Abbott’s BinaxNOW test kits from 12 to 15 months, based on data from the company. CareStart tests distributed through the federal government’s free testing program can also be used three months beyond their stated expiration date, according to COVID.gov.

The California Department of Public Health went one step further in March, saying consumers can use any home test after the expiration date until further notice, as long as the “control” line appears normally. (Your test kit should include guidance on the control line.) Washington state health department officials have also acknowledged that in some cases it may be necessary to use technically advanced but functional tests.

For the latest information on your tests, check the FDA’s website for updates on antigen testing and molecular testing. You may have to calculate the new best before date yourself based on the lot number or date of manufacture stamped on the packaging.

Can I use a test even if it has expired?

If you’re used to ignoring food expiration dates, you may be tempted to do the same with COVID-19 testing. But while some people interpret the dates more broadly, the FDA says it doesn’t use expired kits. dr. Ulysses Wu, infectious disease systems director at Hartford HealthCare in Connecticut, agrees that it’s best to exercise caution because you may not get accurate results using an expired test. “You are more likely to have false negatives than false positives, but those false negatives can create a false sense of security if you are actually positive for COVID,” he says.

Since diagnostic due dates are a “moving target,” your test may actually take longer than the box suggests. But, Wu says, “I’d just follow” [the latest] expiration date and if you’re really concerned or don’t want to throw away, you can always call the company.”

How should I store my home COVID tests?

Time isn’t the only thing that can affect the quality of a COVID-19 test. Humidity and extreme temperatures can also compromise accuracy, Wu says. He recommends keeping medical supplies in a cool, dark place, such as a kitchen cabinet, to keep them stable. Despite the name, your bathroom medicine cabinet isn’t a good place to store medicines and diagnostics because the room often gets hot and humid, Wu adds.

Extreme cold is also something to avoid. When the US government first began distributing free home test kits last winter, some people feared that the liquid reagents used in the diagnostic process could freeze during delivery. While the FDA says this isn’t something to worry about, tests are intended to be used in environments between 59°F and 86°F. So if yours gets cold in transit, give it a let it warm up for a few hours (in the unopened box) before wiping.

And while it may be tempting after recent supply chain problems, Wu recommends keeping a huge stash of tests on hand. It’s good to have a few around in case someone in your home is exposed to the virus or develops symptoms, but there’s no need to buy a lifetime supply right away, he says — both because they may expire before you can use them, and because it makes it harder for others to get the supplies they need.

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Write to Jamie Ducharme at jamie.ducharme@time.com.

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