As the temperatures are dropping, the risk of getting a false-positive result when taking a Covid-19 self-test increases, warned microbiologist Herman Goossens of the University of Antwerp.
Goossens was the head of Belgium's Testing Taskforce until September, but he took to Twitter to share his surprise about the fact that all those present at his Christmas party last weekend tested "faintly positive."
"Celebrated Christmas with (grand)children yesterday. Windows open and tested everyone outside (8°C) before entering the house," he said.
"Everyone faintly positive. Re-tested everyone at room temperature: everyone negative," Goossens added. "Beware of a false-positive result in winter. This is a known problem."
Gisteren kerst gevierd met (klein)kinderen. Ramen open en iedereen buiten (8°C) getest voor betreden woning. Ontstentenis: iedereen zwak positief. Iedereen opnieuw getest bij kamertemperatuur: iedereen negatief. Pas op voor vals positief resultaat in de winter. Gekend probleem.— Herman GOOSSENS (@ProfHGoossens) December 20, 2021
With "a known problem," Goossens refers to a study that he himself commissioned in early 2021. "It showed that self-tests at temperatures of 2 to 4°C produced false-positive results."
"However, I was astonished that this was also the case at 8 degrees," he told Het Nieuwsblad, adding that is not (yet) clear what causes these incorrect results.
"Perhaps a chemical reaction occurs at temperatures that causes such a line on the self-test. That would have nothing to do with the virus. But we are still in the dark about that," said Goossens.
He advises everyone to store and carry out self-tests at room temperature only. "Store the test in your pharmacy cupboard. Not too hot either, because we know that the tests lose their sensitivity at temperatures above 37 degrees. And as this weekend proved: only use at room temperature too."