Heat and humidity could affect rapid antigen COVID-19 tests

Store rapid test at room temperature

SAN ANTONIO – Expecting a COVID-19 test in the mail? Don’t leave it in your mailbox too long, experts say. Heat and humidity could affect its accuracy.

Bexar County’s current COVID-19 risk level is marked as “high” and “worsening” after nearly 300 people with positive results were hospitalized.

As of Wednesday afternoon, the seven-day moving average is 945 cases.

“The current situation in San Antonio is quite alarming to me and to other medical professionals that have to take care of COVID patients,” said Dr. Fred Campbell with UT Health San Antonio.

The last time Bexar County reported 1,000 cases in a day was in early February of this year. Hospitalizations, however, were a lot higher then, with 969 patients.

“The current variants are not as severe as previous ones when it comes to affecting already vaccinated individuals and causing death and serious illness,” Campbell said. “So, we don’t have to worry as much about highly vaccinated individuals as we do those who have not been vaccinated.”

According to data, Bexar County has 1,455,493 people who have been fully vaccinated, and 548,228 have their booster shot.

“Right now, it appears that there are increasing numbers, and those could conceivably have something to do with not using masks and social distancing when someone is inside an enclosed space,” Campbell said.

The Biden Administration released its third round of free at-home COVID-19 tests this week. People can order eight free rapid antigen rests. However, doctors warn about the accuracy of results due to high heat and humidity.

“The manufacturers of home tests are recommending that patients not use them if they’ve been exposed to temperatures of less than 36 degrees or greater than 86 degrees Fahrenheit,” Campbell said. “I have reason to believe that the temperature within a mailbox, particularly in San Antonio, is going to get much higher than that.”

According to the FDA, rapid antigen tests are “not designed to withstand moisture, extreme humidity, or extreme temperatures.”

The liquid inside the vial is made up of proteins and can be compared to an egg. When cooking an egg, the heat causes the molecules to vibrate faster, denaturing or partially destroying the protein.

“The same thing will happen (with the test),” Campbell said. “It will change its nature and make it unreliable to use that home test.”

While each brand is different, COVID-19 rapid tests should be stored in a dry and room temperature location for best results.

To find a local testing location, click here.

For the most up-to-date list of pop-up clinics, click here.


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About the Authors

Alicia Barrera is a KSAT 12 News reporter and anchor. She is also a co-host of the streaming show KSAT News Now. Alicia is a first-generation Mexican-American, fluent in both Spanish and English with a bachelor's degree from Our Lady of the Lake University. She enjoys reading books, traveling solo across Mexico and spending time with family.

Valerie Gomez is lead video editor and graphic artist for KSAT Explains. She began her career in 2014 and has been with KSAT since 2017. She helped create KSAT’s first digital-only newscast in 2018, and her work on KSAT Explains and various specials have earned her a Gracie Award from the Alliance for Women in Media and multiple Emmy nominations.

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