Do at-home COVID tests still work if they get cold? What if they freeze in my mailbox?

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After weeks of dramatically-rising COVID case numbers, empty shelves and apologetic drugstore staff, Americans are now getting free at-home COVID tests mailed to them. Under the Biden Administration's new program 1 billion tests have been ordered for distribution through the United States Postal Service, or you can purchase tests yourself and get reimbursed for up to eight of them through your private insurer.

But there's a problem: These tests contain a liquid component. And arctic blasts have been sending cold fronts and freezing temperatures these last few weeks down from Canada all the way to Florida.

What happens if your test arrives and you can't get to your mailbox right away?

Is it safe to leave tests in your car in freezing weather if you picked them up or bought some and have a few more errands to run? What then?

Short answer: Probably. Most of them are still perfectly fine -- it depends on which brand of test you have -- but make sure all the components are safely back up to room temperature by leaving them out and unopened for at least two hours before you use them. Here's what you need to know.

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Do COVID-19 tests work if they freeze?

According to the U.S. Food and Drug Administration's new guidelines, "Since shipping conditions may vary, test developers perform stability testing to ensure that the test performance will remain stable when tests are stored at various temperatures, including shipping during the summer in very hot regions and in the winter in very cold regions."

Best thing to do is get 'em inside as soon as possible. Don't leave them in your mailbox any longer than you have to, don't leave them in your car overnight, and store them in a dry, room temperature location that doesn't go through a lot of temperature and humidity changes, such as a bathroom shelf or kitchen counter.

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How can I tell if my COVID test is damaged?

Once you bring your test out of the cold, leave it unopened at room temperature for at last two hours before opening it, according to the FDA.

When you perform the test, as long as the test line(s) appear as described in the instructions, "you can be confident that the test is performing as it should," the FDA's website says. If you've performed the test correctly and the line(s) doesn't appear in the time frame the instructions say it should, "then the results may not be accurate, and a new test is needed to get an accurate result."

Also, avoid using tests that have frozen more than once. Dr. Anne Zink, Alaska's chief medical officer and someone who should know about cold, said that based on manufacturer information so far, "we think it is likely the tests will work after one freeze cycle."

Can cold weather affect the results of my COVID-19 test?

The reagent in COVID-19 tests may be permanently damaged after exposure to extreme temperatures, but they're much more susceptible to very high temperatures than very low, according to Dr. Amy Mathers, associate professor of medicine and pathology and associate director of clinical microbiology at the University of Virginia School of Medicine.

Dr. Mathers told TODAY that while very high temperatures can denature the proteins in the reagent chemicals in the tests, COVID-19 tests still may be usable as long as the liquids aren't frozen. “If you warm them back up to room temperature when you run them, they do seem to work quite well,” she said.

When it comes time to take the test, do it inside, out of direct sunlight, and in room temperature. Your kit's instructions will tell you its preferred range of room temperature.

Can cold temperatures cause a COVID test to give a false positive or negative?

Again, it depends on the test.

Lucira listed the results of their extreme temperature testing in their test's instructions sheet (see below) and one of them did return an invalid result, but an additional kit worked. Ellume says their tests, if damaged, return a "Test Error" result rather than a false positive or negative.

If you receive a result you're not sure about, take an additional test, especially if you've been exposed to someone who tested positive or you've been in a high-risk situation recently. You may also consider getting a PCR test, which takes longer and can't be done at home but is more sensitive.

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Here's a look at what some of the common at-home COVID-19 tests have to say about extreme temperatures.

Abbott's BinaxNOW

Abbott recommends that their tests remain between 35.6 and 86 degrees Fahrenheit, and advises not to freeze them. "Test kit reagents must be at room temperature before use."

But a spokesperson for Abbott told Washington D.C.'s WUSA that if the test is stored outside the temperature range "for a relatively short period of time -- for a couple of hours up to a day or two -- it will be fine to use" once it's warmed back up.

Acon's Flowflix COVID-19 Antigen Home Test

Flowflex tests should be stored at temperatures between 36 and 86 degrees. The documentation says DO NOT FREEZE and offers no indication if allowing a frozen test to thaw will work.

BD Veritor At-Home COVID-19 Test

The BD Veritor test should be stored between 35 and 86 degrees before use, and performed indoors between 59 and 86 degrees.

Cue COVID-19 Test

Cue's tests should be stored between 59 and 86 degrees before use, and performed indoors between 59 and 86 degrees.

Ellume COVID-19 Home Test

Ellume's product information does not mention anything about extreme temperatures, but it does suggest storing the test between 36 and 86 degrees.

But one of their test's features is a "Test Error" result that lets you know if there was a problem with testing, such as insufficient swabbing, that might otherwise result in false negative results in other tests. And according to the FDA's Emergency Authorization information for Ellume's at-home test, damage from extreme temperatures may trigger a "Test Error" result.

iHealthLab's COVID-19 Antigen Rapid test

According to iHealth's website, test kits should be stored at temperatures between 36 and 86 degrees. "Any extended exposure of the test kit to temperatures beyond this range may affect quality of test results." They suggest that if you can't be home when you expect the kits to be delivered, "it is recommended that you arrange for someone to be home at or near time of delivery to receive the test kit."

InBios SCoV-2 Detect™ IgG Rapid Test

InBios warns that their test should not be frozen or refrigerated but has a much harsher warning about exposing it to temperatures over 86 degrees, saying it "can impact the performance of the test and should be minimized." Safe storage temperatures are 59 to 86 degrees.

Intrivo's On/Go COVID-19 Test

On/Go tests should be stored between 33.8 and 86 degrees. Tests should still perform if they've been exposed to cold temperatures as long as none of the test components have been harmed, according to an Intrivo representative, and the liquid in the vial in the test is brought to room temperature first.

Lucira CHECKIT COVID-19 Test Kit

Lucira straight up gives you the results of their extreme temperature testing in the instruction manual, with tests that left their kits freezing for 24 hours without problems. "These functional results demonstrate that there was no impact to the performance of the kits when exposed to several temperature and humidity conditions, including below freezing."

Quidel's QuickVue-At-Home

QuickVue tests should be stored between 59 to 86 degrees. But according to a statement the company sent out to the media, the company "has performed studies that demonstrate the product performs as expected under different temperature conditions (i.e., heated and frozen conditions) encountered during shipping."

SD Biosensor

SD Biosensor should be stored in temperatures from 36 to 86 degrees. Their instructions advise not to freeze the kit.

C. A. Bridges is a Digital Producer for the USA TODAY Network, working with multiple newsrooms across Florida. Local journalists work hard to keep you informed about the things you care about, and you can support them by subscribing to your local news organization. Read more articles by Chris here and follow him on Twitter at @cabridges

This article originally appeared on Palm Beach Post: COVID-19 at-home tests: What happens if they freeze in cold weather?