(CNN) — Rapid antigen Covid-19 tests, better known as home tests, have become more common in households across the country as supplies have increased. These tests are designed to give you results in less than 30 minutes from the comfort of your own home.
But if you have several boxes of them stored away, perhaps left over from winter’s Omicron surge or from the federal program that sends up to eight free tests to US households, you might wonder whether they’re safe and accurate to use beyond the expiration date on the package.
The US Food and Drug Administration, which authorizes these tests, says on its website that it “does not recommend using at-home COVID-19 diagnostic tests beyond their authorized expiration dates. COVID-19 tests and parts they are made of may degrade, or break down, over time. Because of this, expired test kits could give inaccurate test results.”
But as manufacturers change the expiration dates for some tests, many are left wondering if it’s that simple.
Dr. William Schaffner, professor in the Division of Infectious Diseases at Vanderbilt University Medical Center, weighed in.
CNN: What exactly are rapid antigen tests?
Dr. William Schaffner: Rapid antigen tests detect tiny, microscopic amounts of protein from the virus. So they actually detect the virus itself. These diagnostic tests quickly detect fragments of proteins found on or within the virus by testing samples collected from the nasal cavity using swabs. One of the main advantages of an antigen test is the speed of the test, which can provide results in minutes. However, antigen tests may not detect all active infections, as they do not work the same way as a PCR test.
CNN: How do the FDA and the manufacturers of the tests decide expiration dates and when to extend them?
Schaffner: Since it takes time for test manufacturers to perform stability testing, the FDA typically authorizes at-home Covid-19 tests with an expiration date of about four to six months from the day the test was manufactured, based on initial study results.
Once the test manufacturer has more stability testing results, such as 12 or 18 months, the test manufacturer can contact the FDA to request that the FDA authorize a longer expiration date. When a longer expiration date is authorized, the test manufacturer may send a notice to customers to provide the new authorized expiration date, so the customers know how long they can use the tests they already have.
CNN: Can you use an expired test?
Schaffner: A word of background: When the tests were first given the green light, when they were approved by the Food and Drug Administration, one of the things that the FDA asked the test developers to do is say, “OK, if I have the test at home and I have them on the shelf or on my bookshelf, for how long will they still be accurate?” A perfectly reasonable question. And of course, in the beginning when the tests were first developed, the manufacturers waited let’s say three months or six months, and then they went to the Food and Drug Administration and said, “here is the data.”
They showed that they still work after three months, and the FDA said “good,” and for those early tests, you put on that you have an expiration date of three months, but that’s just because that was the duration that was tested.
Now, the same manufacturer keeps their tests on the shelf for six months, shows that they still work and goes to the FDA and says “they work up to six months,” and the FDA says “great.” Now, you can put six months on your box when you sell it.
So you could have gotten a test from the same manufacturer and a shorter and a longer expiration date, depending upon when the actual test was made and delivered to the store or sent to you by the federal government. We have tests now that have been shown to be good for a year and I think some probably even longer. In other words, these are very, very stable tests.
Now, if I have a test that expired last week, will it still be accurate this week if I use it? And the short answer is yes. As long as you haven’t abused the test in some way, put it in a deep freeze or left it out in the sun or something like that. Sure. We can rely on the results of the test.
CNN: Can people still access free testing in other places?
Schaffner: Many [testing sites] have closed, or they’re available to you in a much more restricted range of hours. And that’s obviously because of availability. Rapid tests are available. That’s taking a lot of the pressure off the testing locations where PCR testing was available, so that’s much less widely and quickly available. Your physician can still send off a PCR test to your health care provider, but it may take a week for the results to come back, and it will be paid for by your insurance. But if you’re looking for free testing, I think those testing sites have been much more restricted now than they once were.
CNN: What’s the most important thing people should know in order to get accurate results for rapid tests?
Schaffner: The instructions. I have found as I have looked at them — and I don’t pretend to have looked at every test box that’s out there — but I’ve looked at a number of them. The instructions are really very clear. They have illustrations, and my suggestion is do it exactly right. It’s not complicated, but do it exactly, no deviation, as the instructions say, and then you can be quite reliant on the results.
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