Study Finds False-Positives in Over 40% of Positive COVID Results From Sample of 900,000 Rapid Tests

A new study reveals that more than 40 percent of the positive results from a large sample of rapid antigen tests are false-positives, a finding that comes at a time when provinces are increasingly relying on the rapid tests to form COVID-19 response strategies.

The study, conducted by the University of Toronto’s Rotman School of Management, was published in the peer-reviewed Journal of the American Medical Association (JAMA) on Jan. 7, 2022. The researchers studied the results of roughly 900,000 rapid antigen tests taken in over 530 workplaces across Canada between Jan. 11 and Oct. 13, 2021.

During this period, the country experienced two major COVID-19 waves driven by the Delta variant, recording 1,322 positive rapid test results, or 0.15 percent of the total number of tests. Among the positive cases, 1,103 individuals were asked to take a polymerase chain reaction (PCR) test for further confirmation.

The study found that 462, or around 42 percent, of those 1,103 positive test results were false, or 0.05 percent of the over 900,000 results.

“These results inform the discussion of whether rapid antigen tests will result in too many false-positives that could overwhelm PCR testing capacity in other settings,” the researchers wrote.

They said their findings reflect the importance of having “a comprehensive data system to quickly identify potential issues,” though they also noted that the overall rate of the false-positive results compared to the total rapid antigen test screens was “very low.”

“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,” they wrote.

Of the 462 false-positive results, 278 (60 percent) were undertaken in two workplaces 675 kilometers apart by different companies between Sept. 25 and Oct. 8, 2021. The researchers said all of these false-positive test results were caused by a single batch of Abbott’s Panbio COVID-19 Ag Rapid Test Device, likely due to manufacturing issues rather than implementation.

Tests being administered too early or too late in the infectious stage, or being done in an incorrect manner, are some other reasons that could contribute to false-positive results, the study says.

Correction: A previous version of this article misstated the number of positive cases from rapid antigen testing that also underwent PCR testing. Of the 1,322 positive cases found in the original sample, 1,103 underwent PCR testing for further confirmation, and 462 of those, or around 42 percent, were false-positives. The Epoch Times regrets the error.