Experts attribute the false negatives to other possible factors: no test is 100% accurate, people may not be administering them correctly, or people are testing too early to detect their COVID-19 infections.
A look at several brands of COVID-19 at-home rapid antigen tests, which can be found for purchase online and in some stores when in stock. Brands featured include BinaxNow, iHealth, On/Go and QuickVue. Photo by Tim Brown/StaffCHICAGO — Jackie Kramer thought she had COVID-19 late last month.Yet the Andersonville woman kept testing negative, over and over again. She took several PCR tests and rapid, at-home COVID-19 tests every day for a week.
“You should never do just one test,” said Dr. Emily Landon, hospital epidemiologist at University of Chicago Medical Center. “There’s a reason there’s two tests in the box.”It can take time for the amount of the virus in a person’s body to reach a high enough level that an at-home test would detect it, she said.
Lisa Guo knows she was fortunate to have several COVID-19 tests on-hand last month, after she was exposed to a co-worker with COVID-19. “I knew I had something and I was pretty sure it was COVID, and that’s why I kept testing,” said Guo, who was sick for about two weeks but has since recovered. She also tested repeatedly because of guidance from her father, who is an emergency room doctor, she said.
At-home tests also, generally, aren’t as effective when used by asymptomatic people, such as after an exposure, Landon said. Those people should likely get PCR tests instead, or, if they’re going to use at-home tests, take them every other day starting three days after the exposure until nine days after.
People who test positive on at-home tests likely have so much virus in their bodies that they’re more likely to be contagious than those who test negative, even if they have COVID-19, he said.