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People who stocked up on at-home COVID-19 tests during this past winter's Omicron surge may have expired test kits on hand. But before tossing them in the trash, check to see if their shelf-life has been extended, as the FDA has updated expiration dates for some tests based on new data.

Among those tests are the Abbott BinaxNOW and the iHealth test, two of the most popular rapid at-home tests, which received 3- or 6-month extensions, depending on lot number.

Overall, 8 of the 20 at-home tests had their shelf-life extended, and the 3- to 6-month extension appears to be typical. Shelf-life now ranges from 4 months for the Cue Health home test, to 18 months for Celltrion's DiaTrust test.

"These are tests you don't have to buy again, that you don't have to spend money on, that you don't have to order again from the government," said Emily Volk, MD, president of the College of American Pathologists. "From a resource utilization perspective, I think it's very positive."

FDA conducts stability testing to determine the shelf-life of tests. The agency said it typically with a shelf-life of about 4 to 6 months from the day the test was manufactured, and that date may be extended later as additional data are collected.

"The FDA is continuing to do studies and make sure that the tools that are available are appropriate and safe," Volk said.

Some popular tests, including Becton, Dickinson and Company's Veritor and the Quidel QuickVue, have not yet received an extension on their expiration dates, however.

What could go wrong with tests that are truly expired? Volk said a chief concern would be chemical degradation of the reagents.

"If certain chemicals sit out too long, they can change their chemical composition and not work as expected," she said. That would include the liquid developing solution that's mixed with your nasal swab sample and dropped onto the card, as well as the card itself, which has molecules embedded in it that are meant to react with the COVID-19 virus, she noted.

Volk wouldn't recommend using tests that have gone beyond their shelf-life. Most likely, these tests could cause false-negative results if they're not working properly.

"As a physician, I wouldn't recommend to anybody to use an expired test, just like I wouldn't want them using any kind of over-the-counter medication or prescription medication that's expired," she added.

However, she said that she's not worried about FDA's extension of certain tests because those recommendations have data behind them.

"I don't have any concerns, as long as the tests have been stored according to the instructions for storage, which generally means avoiding extremes of heat and cold and avoiding dampness," she noted.

Some concerns have also been raised about whether the at-home tests are still accurate in the face of the new Omicron sublineages, including BA.4 and BA.5. Volk said it's believed the tests are still very effective, as manufacturers have focused on including parts of the virus that are more stable in their tests.

"At some point it is possible that the virus will mutate so much that we can't detect it with our current tests," she acknowledged. "That's certainly feasible down the road, but right now, we're not seeing that."

Volk cautioned that, whether a test is expired or not, patients shouldn't rely on results that just don't make sense.

"If you've been exposed to somebody with COVID, and you have symptoms, and your home test is coming up negative, you really should go get a laboratory PCR test," she advised.

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