TORONTO — There’s good news for people needing to find out their COVID-19 status quickly. A new study finds the likelihood of having a false positive result from a rapid antigen test is very low.
Researchers from the University of Toronto’s Rotman School of Management say PCR tests are currently the gold standard for COVID-19 testing because of their low error rate. However, PCRs take a few days for results to come in, while rapid antigen tests take approximately 15 minutes. Having a false positive, however, could impact ongoing care, as healthcare workers and first responders with false positives still have to isolate according to CDC guidelines.
The study used rapid antigen tests to screen asymptomatic Canadian workers twice a week. On-site testing was available from Jan. 11 to Oct. 13, 2021. During this time, Canada experienced two Delta variant waves occurring from March to June and from August to October.
If a worker tested positive for COVID-19, they had to take a PCR test to confirm the results. Study authors defined a false positive as having a positive result on a rapid 15-minute test but a negative result on a PCR test.
Which rapid tests may be less reliable?
More than 900,000 rapid antigen tests were distributed across 537 workplaces. Less than one percent (1,322 tests) came back positive. Of those that tested positive during the rapid antigen test, researchers confirmed that 462 were false positives.
Sixty percent of these false positives came from two workplaces using Abbott’s Panbio COVID-19 Ag-Rapid Test Device. The researchers explain that the false positives may have been from faulty issues with the test or the timing of the test. A rapid antigen test could be inaccurate if someone uses it too early or too late in the infectious stage.
“With the ability to identify batch issues within 24 hours, workers could return to work, problematic test batches could be discarded, and the public health authorities and manufacturer could be informed,” the research team explains in a university release.
The study is published in the Journal of the American Medical Association (JAMA).