Due to "quirks" in the regulatory process for at-home Covid-19 tests, expiration dates on the tests are not always accurate. Writing for the New York Times, Tara Parker-Pope explains what to do before discarding a test that appears to be past its expiration date.

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Why the expiration for at-home Covid-19 tests 'can be a moving target'

While at-home Covid-19 tests do expire, "the actual expiration for a box of tests can be a moving target," Parker-Pope writes. Before discarding a home test that seems to be expired, she recommends doing some "homework."

Specifically, Parker-Pope explains that the range of expiration dates can vary widely depending on the type of test; while one test could expire in six months, another could expire in 15 months—even though the tests use similar technology to detect antigens.

According to Michael Mina, an expert in home-test technology and chief science officer for eMed, these variances are largely the result of quirks in the regulatory process rather than any meaningful differences in the stability of the different tests.

As Parker-Pope explains, FDA varies in its requirements for testing a product's shelf-life, but for rapid at-home Covid-19 tests specifically, the agency requested manufacturers provide real-time data. As a result, the only way to find out how long a test will last is to wait for months so test makers can perform stability studies to determine the tests' shelf life.

"As a result of this requirement, a home test might have a six-month expiration when it's first authorized, but as more time passes the test maker collects more data and seeks an extension to the original shelf-life date," Parker-Pope writes. "That means you might have a test at home that's passed its expiration date, but if you call the company or dig through the [FDA] authorization letters, you'll find it has changed."

"When the test is new, it has a six-month expiration," Mina said. "But once you get to six months, the FDA may extend it. That's been happening a lot, which is exceedingly confusing."

What should you do if you think a test is expired?

Each test should have a mark with a manufacturing date and an expiration date. According to an FDA spokesperson, individuals with questions about expiration dates for at-home tests can view the various regulatory documents that extend a test's shelf life to determine whether a test is actually expired. The website has a section for antigen tests and molecular tests.

While health experts don't want to advise consumers to use expired tests, Parker-Pope writes, they also want to prevent people from throwing away an expensive test if it is still functional. 

"Many people now have a small inventory of tests at home," Mara Aspinall, an expert in biomedical diagnostics at Arizona State University, said. "It would be a pity if somebody has symptoms, but they don't use a test because it's a few days out of date. If a test is days out of date, it's highly likely it's still effective. If it's months out of date, it's very important to check the website to see if the date was extended."

According to Parker-Pope, there are practical ways to ensure the longevity of the tests. "Keep it at room temperature in dry conditions; don't let it freeze or become exposed to heat, which can interfere with the accuracy of the test," she writes. "If you're planning to order more free government tests, do so now before the summer weather arrives so they're not sitting for hours in a hot mail truck."

Further, when shopping for at-home tests, consumers should always check expiration dates in the store to ensure that they are not about to expire.

"And whether you're using a new test or one that is a little past its expiration date, follow the instructions carefully—and make sure the control line shows up quickly, which is an indicator that the test is still working," Parker-Pope adds.

"The reality is that these tests are very, very stable," Mina said. "My expectation is that most of them, if not all of them, eventually will have a two-year expiration date at least. If the control line is showing up and it's within 18 to 24 months of the manufacture date, you should assume the test is working." (Parker-Pope, New York Times, 4/5)