The U.S. government has provided free COVID-19 test kits on multiple occasions, which means a small stockpile may be forming in your medicine cabinet. But these rapid antigen tests don’t last forever and results from an expired home-test kit may be unreliable, says Omai Garner, PhD, director of clinical microbiology for UCLA Health.
Unless, of course, the expiration date has been extended, as is the case with many of the free, government-provided test kits. The U.S. Food and Drug Administration announced recently that expiration dates have been updated on testing kits from a variety of manufacturers. The agency issued a table for Americans to check the status of COVID-19 home tests.
Once past the updated expiration date, results from home test kits are unreliable, Dr. Garner says, adding that it’s likely that the solution used to identify viral proteins in the nasal swab sample loses effectiveness with time. The amount of time a test is good for varies by manufacturer – some expiration dates may be six months or a year after production; others may be much less.
The FDA says extended expiration dates for government-issued COVID-19 tests “means the manufacturer provided data showing that the shelf-life is longer than was known when the test was first authorized.”
The federal government has announced it will stop providing these free COVID test kits effective Friday, Sept. 2.
Storage temperature matters
COVID-19 antigen test kits are temperature-sensitive, too — something important to remember during hot summer days. Most COVID tests need to be stored at temperatures of less than 86 degrees.
“That’s no problem if they’re in your temperature-controlled house,” Dr. Garner says. “But if you’re keeping them in the trunk of your car or keeping them in an outdoor storage shed — the temperatures in Los Angeles can easily go over 100 in the summer and that would make the tests not perform correctly.”
Even allowing test kits to sit in your mailbox on a hot afternoon until you get home from work would make them unusable, he says. Heat damages the chemicals used to identify viral proteins.
“These tests aren’t to be outside the temperature window at all, period,” he says.
Some test kits can be refrigerated; others can’t, Dr. Garner notes. Temperature specs are noted on the package.
Is an expired test better than no test?
If cases are surging and test kits aren’t easy to come by, it could make sense to use a recently expired test. A kit that expires on Sept. 27, for example, is probably still good on Sept. 28, Dr. Garner says.
“If we’re surging and you have some recently expired kits, of course that’s going to be better than no test at all,” he says. “But if we’re not surging and you could just go to the store and get another set of tests, it’s better to do that.”
When should I test?
In individuals who are vaccinated and boosted, however, it may take a few days of infection before viral proteins reach a level detectable by an antigen test.
“There’s high enough virus count to be contagious, but not high enough to get one of these tests to work,” Dr. Garner says.
People who have been vaccinated and boosted and have symptoms of COVID-19 should plan to test twice. If a symptomatic person performs an antigen test and the results are negative, Dr. Garner recommends retesting 48 hours later.
“That’s why they come in packs of two,” he says. “If the second test comes back negative, you can feel pretty confident that you don’t have COVID-19.”
The PCR test remains the “gold standard” for identifying COVID-19 infection, Dr. Garner says. This lab-performed test, also based on a nasal swab, can detect the virus while viral levels are still emerging.
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