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  • Prolonged exposure to extreme cold and heat may skew the results of at-home COVID-19 tests.
  • All at-home COVID-19 tests should be stored within a certain temperature range, usually 36–86°F (2–30°C).
  • COVID-19 tests contain liquid and other components that, if frozen or too cold for a long time, can skew the results.

As tens of millions of at-home COVID-19 tests from the government make their way to Americans in the mail, many parts of the country are facing sub-zero temperatures.

So what happens if your test kit freezes on the way to your house? Can you still use it?

All at-home COVID-19 tests should be stored within a certain temperature range, usually 36–86°F (2–30°C).

The temperature range for your test will be listed on the instructions that came with the box or on the manufacturer’s website.

Storage of these kinds of rapid antigen tests for extended periods outside this range can produce less accurate results, according to a study last year in the Journal of Clinical Virology.

How much the results are impacted depends on how long the kit has been hot or cold and whether it went through repeated cycles of freezing and thawing.

At-home COVID-19 tests contain liquid and other components that, if frozen or too cold for a long time, can skew the results.

To ensure that the test will work as intended, the Food and Drug Administration (FDA) recommends that people follow the instructions that come with the test or online, which includes temperature and other storage guidelines.

Manufacturers have also developed the tests with temperature fluctuations during shipping in mind.

“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,” the FDA said, “including shipping during the summer in very hot regions and in the winter in very cold regions.”

Dr. Amy Karger, chair of the College of American Pathologists Point-of-Care Testing Committee, thinks we need more independent study of the impact of temperature fluctuations during shipping on at-home tests.

However, “there haven’t been any reports or any evidence to suggest that the kits are compromised by shipping temperatures,” she said. “So I would cautiously say that they should be fine.”

In addition, “a single freeze-thaw isn’t going to destroy the rapid antigen test,” epidemiologist Dr. Michael Mina wrote on Twitter. “[It] may reduce sensitivity a little bit, but not much.”

A spokesperson for Abbott Laboratories, maker of the BinaxNOW test, confirmed this.

“If the test is stored outside the [35.6–86°F] 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,” the spokesperson told Healthline.

If your at-home test arrives in the mail very cold or frozen, the FDA recommends that you “bring the package inside your home and leave it unopened at room temperature for at least two hours before opening it.”

“If you were to perform the test with a kit that’s too cold or too hot, that does affect the accuracy of the test,” said Karger.

Room temperature for most at-home tests is approximately 59–86°F (15–30°C). But again, check the instructions that came with your test.

You probably won’t know if your at-home test froze and thawed several times during shipping, but Karger said there are some signs that a test may not be working properly.

Most tests have a “control” line that should always appear whether you’re positive or negative for the coronavirus.

Karger said if the “control” line doesn’t show up, takes longer to appear than indicated on the instructions or appears before you run the test, you should not rely on the result.

The Ellume COVID-19 Home Test has an internal control that will trigger a “Test Error” result “if the product is exposed to extreme temperature and humidity that could be damaging to the test reagents.”

If you think your test may not be working properly, take another test, either an at-home test or a PCR test.

High temperatures can also cause a problem with at-home COVID-19 tests.

The maximum storage temperature for most COVID-19 tests is 86°F (30°C), but check the instructions that came with the test.

“Very high heat can cause a lot of damage to a rapid antigen test,” wrote Mina on Twitter. “Don’t let your test boil in the sun in the summer… the proteins can fall apart and the test can be irreparably harmed.”

The instructions for some tests also recommend against placing the test in direct sunlight, which may damage the components in the test. This is a good rule of thumb to follow for all tests.

If your at-home COVID-19 test is positive, that’s a good indication that you have a coronavirus infection. For most tests, the chance of a false positive occurring is small.

In this case, follow the Centers for Disease Control and Prevention’s guidelines, including isolating and wearing a well-fitting face mask if you have to be around others.

A negative test indicates that no coronavirus was detected in your sample.

This might be because you don’t have a coronavirus infection. However, a negative result can also happen for other reasons.

“If you get a negative result, especially if you have [COVID-19] symptoms, you should take that negative with a grain of salt,” said Karger.

For example, if you take the test early during a coronavirus infection, the test can give a negative result because the amount of virus in your body isn’t high enough for the test to detect. There could also be a problem with the test kit.

“If you do get a negative result and you’re symptomatic, you should still stay at home,” said Karger.

“You should still behave as if you have COVID and continue to test on a daily basis, for a few days at least, because some people are reporting not turning positive until day three and even four.”