Discussion of whether home covid tests actually expire

Q: Do home Covid tests really expire? I ordered what I was allowed. Now I see they have expiration dates. Some have already expired. What to do? Keep and use, or throw them out?

It’s true that home Covid-19 tests are marked with expiration dates, but the actual expiration for a box of tests can be a moving target. Before throwing away a home test because you think it may have expired, do a little homework first.

Depending on which home test you buy, or receive for free from the government, you might see a range of expiration windows. One test might expire in six months, another in nine months, 11 months or even 15 months. The tests all use similar technology to detect antigens (pieces of viral proteins) from a swab sample — so why do the expiration dates stamped on the boxes vary so widely?

The answer has to do with the quirks of the regulatory process rather than any meaningful differences in the stability of the various tests, said Dr. Michael Mina, a well-known expert in home-test technology and chief science officer for eMed, a company that helps rapid test users get treatment from home.

When it comes to determining shelf life for any product it regulates, the Food and Drug Administration may allow a fast method or require a slower one. For some products, the agency will allow a manufacturer to rapidly simulate conditions — a process called “accelerated dating” — to show how long the item will last sitting in your medicine cabinet, said Mara Aspinall, an expert in biomedical diagnostics at Arizona State University who is also on the board of OraSure, which makes rapid Covid tests. This quick process can allow the manufacturer to determine in a matter of weeks whether a product has a shelf life of a few months or as long as a few years.

But in the case of the rapid home tests, the F.D.A. has asked for real-time data from manufacturers, which is a much longer process. Will a test that sits on the shelf still work after nine months? Twelve months? The only way to find out is to wait for the months to pass so the test makers can conduct stability studies to prove the tests still work over time.

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. 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 F.D.A. authorization letters, you’ll find it has changed. ...