Have you ever been exposed to someone with COVID-19, or had the sniffles, and reached for an at-home test in your medicine cabinet—only to notice it’s way past the expiration date stamped on the box?

Don’t toss the test kit in the trash, says Mansoor Amiji, university distinguished professor of pharmaceutical sciences and chemical engineering.

He says the FDA has extended the shelf life of some common at-home antigen tests by months after new evaluations showed they remain stable for longer than first thought.

When the at-home tests for SARS-Cov-2 debuted, there was a lot of confusion about how reliable they would be for an extended period of time, Amiji says.

To be on the safe side, the FDA chose to be “very conservative” in terms of shelf life, he says. The federal agency initially said the tests expired after six to eight months of manufacture.

But since the first at-home antigen test for COVID-19 came out three years ago this month, test manufacturers have had time to conduct longer-range assessments of shelf stability. 

How to find your test’s expiration date online

In some cases, the FDA approved extending the shelf life of tests by a year or so, Amiji says, adding that some tests retain their efficacy for 24 months after manufacture, with the new average being 20 months.

He says there are a couple of ways to check to see whether the test kit you have is still effective.

The North Carolina Department of Health and Human Services has a user-friendly website where people can use the test brand name and lot number to see if the FDA has revised the expiration date, Amiji says.

The lot number is next to the expiration date and may be a combination of letters and numbers.

Some lots associated with InteliSwab, for instance, had expiration dates extended from October 2022 to January 2024.

People can also go directly to the FDA’s website on expiration dates for a more extensive list of test brands.

The FDA provides a link to products with extended expiration dates. If it says to check the expiration date on the box and that date has passed, throw the test away.

When to test

The FDA says people with possible COVID-19 symptoms should test immediately. 

Those who have been exposed to an infected person but do not have symptoms should wait a full five days after exposure to test themselves.

The federal agency also suggests that people consider testing before coming into contact with someone at high risk for severe COVID-19, older adults and people who are immunocompromised, especially if they reside in an area with a medium to high COVID-19 hospital admission level.

Why expiration dates matter

Amiji says the at-home test kits work by putting antibodies in the test kit solution into contact with material from nasal swabs. If the mucus contains the protein antigen of the SARS-CoV-2 virus, that means infection is present.

“You’re testing to see if the antibody will react to the antigen and produce a color product,” he says.

If the test is past its shelf life, “you’re not going to get accurate results,” Amiji says. “You may get false negatives” even though you are actually infected.

It’s also important to store the at-home tests properly, at room temperature in a dry location, he says.

The FDA recommends that people should leave tests unopened at room temperature for about two hours before being used if they have been delivered in freezing conditions or exposed to heat. 

“Once the package is at room temperature, you may open it and perform the test according to the authorized instructions for use,” the FDA says.

Cynthia McCormick Hibbert is a Northeastern Global News reporter. Email her at c.hibbert@northeastern.edu or contact her on X/Twitter @HibbertCynthia.