UW Study Finds Coronavirus Rapid Tests Are 'Far Less Sensitive'

SEATTLE — Coronavirus antigen tests can be useful at detecting certain infections, but are about 100 times less sensitive than traditional lab methods, according to new research from UW Medicine.

In August, the Food and Drug Administration granted an emergency use authorization for the BinaxNOW rapid test designed by Abbott Laboratories. Unlike PCR tests, which must be processed in a lab, the antigen tests typically return results within 15 minutes.

The federal government bought 150 million of the test kits and shipped them across the country, including millions sent to Washington. While authorized use only includes people within seven days of developing symptoms, UW Medicine said some organizations, like sports teams and nursing homes, have utilized the tests "off label."

Researchers found using the rapid tests as a screening measure for asymptomatic people was much less effective than detecting illness in those with recent symptoms, when patients are most likely to shed large amounts of the virus.

"The Abbott test works surprisingly well, but it will likely miss cases from whom live virus would be detected by other methods," said Dr. Alex Greninger, the senior author of the study.

To contrast the two tests, UW researchers compared antigen results with PCR lab results, finding the rapid tests to be far less sensitive and require a much higher level of virus present to successfully detect infection in 95 percent of cases.

"Although affordable, rapid testing is critical for reducing transmission in this pandemic, it's important to understand how these tests perform and use them appropriately," Greninger said. "There simply aren't enough of these tests yet to enable widespread, repeated screening of the general population."

Read the full study published in the Journal of Clinical Microbiology online.