As COVID-19 tests are being delivered from the government by the U.S. Postal Service, some are concerned that if the tests are left in mailboxes in regions where the temperatures are frigid, the test could be less effective at determining if a person has the virus.

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Most manufacturers of COVID-19 at-home test kits recommend that the tests be stored at temperatures above 35 degrees so that the liquid used in the test does not freeze. If the liquid freezes it can cause a decline in the effectiveness of the test.

According to the U.S. Food and Drug Administration, manufacturers have seen a lot of stability in the tests under varying temperature conditions.

“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,” the FDA said.

According to research by Abbott Laboratories, the BinaxNow tests should be stored in a place that is between 35.6 and 86 degrees and be used at room temperature, Abbott Laboratories spokeswoman Kim Modory told The Washington Post.

Dr. Geoffrey Baird, chair of laboratory medicine and pathology at the University of Washington’s School of Medicine, told USA Today that if the test is in freezing conditions outside for several hours, it may not be reliable.

If the test has been in the mailbox for an entire day, Baird said you should use a PCR COVID-19 test instead. If a test has been in the mailbox in freezing conditions overnight, you should not use it.

“Just as anything with liquid, if it’s chilled or frozen, it changes. That’s the same with these at-home tests,” Baird said. “At a time where temperatures are freezing in most places, it’s safer to choose another test.”

You are more likely to get a false-negative test result if temperature has affected the test, according to research.

Tests should be a room temperature when you use it. If it arrives to your home and is cold, let it warm up on its own inside of your house.

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