NEWS

Can I Use a COVID-19 At-Home Test That Was Left Out in the Cold?

antigen test liquid

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Key Takeaways

  • At-home rapid tests should continue to work if they were left out in freezing temperatures for a short period of time.
  • Bringing the test back to room temperature for at least two hours should make it usable, but heat exposure may damage it beyond use.
  • When in doubt, check if the control line on your tests appears normally per the test’s instructions. If it doesn’t, the test is likely defective.

The federal government is mailing at-home COVID-19 tests to households across the country as parts of the North and Southeast experience cold snaps and snowfall.

Most of the at-home tests authorized by the Food and Drug Administration (FDA) should be stored at 35 degrees or above. Below that temperature, the testing liquid can freeze, potentially decreasing its effectiveness.

COVID-19 test manufacturers take weather changes into account and typically provide a range of acceptable temperatures on the test packaging, according to the FDA. The tests should be performed in an environment that’s around 59–86 degrees Fahrenheit.

“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.

For instance, BinaxNow tests should be stored at 35.6–86 degrees while Ellume says to store its rapid test at 59–95 degrees. Both must be used at room temperature.

How Does Temperature Affect the Tests?

The longer a test sits outside and the colder it is, the greater the likelihood that it will freeze or lose some efficacy. It’s best to bring the package inside as soon as it arrives. If it’s cold outside, let the unopened test sit inside for at least two hours until it reaches room temperature, according to the FDA.

“If it’s sitting outside and you’re in Alaska or in the Northwest—somewhere very cold—and it’s frozen for days, it could be impacted,” Michael Blaivas, MD, FACEP, FAIUM, an emergency physician and chief medical officer at Anavasi Diagnostic, told Verywell. “If you’re in a part of the country where, let’s say, it dipped to 35 degrees yesterday after the carrier dropped it off and didn’t get colder, just let it warm up to room temperature and there really shouldn’t be any issues with it.”

Tests that are exposed to heat, on the other hand, may be irreversibly damaged. Just as eggs firm up and Jello liquifies in heat, the proteins in the antigen tests can disintegrate or change form.

In a study of 11 commercially available antigen tests, researchers found that storage at 98 degrees produced false negatives, while those stored at 39 degrees had a greater risk of producing a false positive.

“You could basically inactivate all of the key active ingredients when the temperature goes too high,” Blaivas said. “Then you get a test that’s false negative.”

The heat, he said, is a “bigger enemy” to the active ingredients in these tests than freezing temperatures. The longer the tests sit in a hot environment, the greater the chances of the ingredients breaking down. While this may not be an issue for many Americans during the winter, leaving a test sitting in a warm spot, like near a space heater, could impair its effectiveness.

Should You Still Use the Test?

The best way to check whether your test has been too damaged is to ensure the “control” line still appears as it’s supposed to.

Be sure the liquid reagent in the test isn’t frozen when you use it. You can simply feel the container—if it’s cold to the touch, wait a bit longer. If the test lines do not appear in the correct location or within the time described in the instructions, the results may not be accurate. It’s best to get a new test.

“If it was out in the cold overnight and didn’t freeze too much, as long as the control line comes up, I would have more confidence that that’s an indicator the test is going to be okay,” Blaivas said.

The instruction manual included with your test will have specific details on the suitable conditions for taking your test. While designed to be used at home, these rapid antigen tests are adapted from more complex laboratory tests and leave little room for error, Blaivas said.

A good rule of thumb for testing throughout the pandemic also applies here—trust a positive result. False positives are far less common than false negative results. Plus, extreme weather that causes damage to a test is more likely to disrupt the test’s sensitivity, meaning you’re more likely to get a false negative.

A review of the efficacy of BinaxNOW tests administered by professionals found that those used below the recommended range of 46–58.5 degrees were only able to detect two-thirds of positive cases.

“If you’re sitting in a hot spot, you’ve got symptoms and you feel horrible, everybody in your family has COVID, and you get a negative test, you really can’t trust that,” Blaivas said. “You need to get a molecular test.”

If you’re experiencing symptoms of COVID-19 and receive a negative result from a rapid test, it’s best to follow up with a more sensitive PCR test to confirm your infection status.

If there's a problem with a COVID-19 test, you can report the incident through the MedWatch Online Voluntary Reporting Form.

What This Means For You

To avoid damage to your rapid antigen tests, experts recommend storing and using them at room temperature. If a test has been sitting in the cold, let it rest, unopened, for at least two hours to bring it to room temperature before using it.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Food and Drug Administration. At-home COVID-19 diagnostic tests: frequently asked questions.

  2. Haage V, de Oliveira-Filho EF, Moreira-Soto A, et al. Impaired performance of SARS-CoV-2 antigen-detecting rapid diagnostic tests at elevated and low temperatures. J Clin Virol. 2021;138:104796. doi:10.1016/j.jcv.2021.104796

  3. Pollock NR, Jacobs JR, Tran K, et al. Performance and implementation evaluation of the Abbott BinaxNOW rapid antigen test in a high-throughput drive-through community testing site in Massachusetts. J Clin Microbiol. 2021;59(5):e00083-21. doi:10.1128/JCM.00083-21

By Claire Bugos
Claire Bugos is a health and science reporter and writer and a 2020 National Association of Science Writers travel fellow.