Can at-home COVID-19 tests survive Minnesota's frigid temperatures?

Minnesotans are receiving free COVID-19 at-home test kits offered by the federal government, with many left in mailboxes or on porches in frigid February temperatures.

But the test boxes say they should be stored between 36 and 86 degrees.

Because the Twin Cities has seen only one day in the last 10 with a high temperature above 36 degrees, will the tests deliver accurate results if they've been out in the cold?

The federal government is distributing several test brands, and although each one is slightly different, most contain a liquid known as a reagent that can freeze in cold temperatures.

The Food and Drug Administration said the at-home tests can still be used if they have been out in cold weather.

"In order to ensure appropriate test performance with a test that is delivered to you in below-freezing temperatures, you should bring the package inside your home and leave it unopened at room temperature for at least two hours before opening it," the agency said in a statement.

However, the agency did not explicitly say tests would still be good if, say, left in a curbside mailbox in 10-below weather for six to eight hours.

The FDA said manufacturers have done 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."

One Minnesota researcher said more rigorous independent testing needs to be done.

"I would advise based on what I know now, not having good rigorous data, [that] I don't think people should be too worried because I don't see any good data that suggests that it should be tossed," said Dr. Amy Karger, a clinical pathologist with the University of Minnesota Medical School and M Health Fairview.

"But I do suggest that if people can get them out of the cold, the sooner the better," she said.

The test results do have a built-in indicator, sometimes called a control line, that signals the test worked.

"If the control line doesn't show up when you are testing, that shows you that the test is not working properly," Karger said.

The test kit includes instructions on which lines should appear.

"If the line(s) do not appear in the correct location(s) and within the correct time as shown in the test instructions when you perform the test, then the results may not be accurate, and a new test is needed to get an accurate result," the FDA said.

Consumers can sign up for e-mail or text shipping alerts when ordering the four free tests from the federal website, giving lead time to prepare for the tests' arrival.

Last week, the White House said that 60 million households have requested the tests. It is unclear how many have arrived or are on their way to Minnesota because the United States Postal Service doesn't have regional breakdowns, an agency spokesman said.

Abbott, which makes the BinaxNOW COVID-19 test, said its tests should work if left outside for a "short period of time," including up to two days, but the test should be performed at room temperature.

Temperature is not the only thing that affects reliability. Each test has detailed instructions, and things can go wrong if the sample is not collected correctly or if the reagent is not properly prepared.

"Home tests are useful because they do encourage people to get tested more often," Karger said. "However you need to understand that there are a lot of things that can cause false negatives or inaccurate results."

The omicron variant is not as likely to be detected by a home test in the first few days of infection, Karger said.

"The tests are useful especially if they turn positive," she said. "There are lot of things that can cause false negatives, so take negatives with a grain of salt."

Vault Health has been sending at-home saliva tests to Minnesotans since November 2020 and says its tests are not affected by extreme cold or heat.

The Minnesota Department of Health announced another 6,617 COVID-19 cases Friday. It reports only infections detected by testing laboratories, including Vault. The antigen at-home tests are not reported to the state.

The state's testing positivity rate continues to fall and now stands at 19.2%, from an omicron-driven high of 23.6%.

Nearly 1.4 million Minnesotans have tested positive for COVID-19, the Health Department reports. There have been 11,599 deaths, including 38 announced Friday.

On Thursday, 1,260 people were hospitalized with COVID-19 complications, including 194 in intensive care. Both numbers have been trending down.