Utah halts state, on-site rapid testing after analysis finds ‘higher than expected’ false negatives

Epidemiologists raised questions about the reliability of state-offered GenBody rapid tests. An analysis found an excessive number of negative results among people who tested positive on PCRs.

(Rachel Rydalch | The Salt Lake Tribune) A COVID-19 testing site is pictured along Guardsman Way in Salt Lake City on Thursday, Feb. 3, 2022.

The Utah Department of Health announced Sunday that it will temporarily halt the use of on-site rapid antigen tests at all state-operated COVID-19 testing sites beginning Monday.

The move comes after data analyzed by UDOH raised questions about the reliability of GenBody rapid antigen test results. The rapid tests were offered at sites run by UDOH mobile test teams, TestUtah and TourHealth.

“We think we’re doing the right thing by halting the use of these until we can understand better why they’re not performing as well as other tests,” UDOH deputy director Michelle Hofmann said Sunday afternoon.

An analysis of about 18,000 Utah residents who received both GenBody rapid tests and PCR tests at state sites on the same day found that, of those who tested positive on a PCR test, more than half tested negative on the GenBody tests, UDOH announced Sunday.

Even while acknowledging that rapid antigen tests are less likely to identify positive individuals, UDOH deemed this discrepancy to be “higher than expected.”

By comparison, another analysis was conducted comparing results of those who received both a PCR test and a BinaxNow rapid antigen test. That analysis yielded better results, with less than one-third of patients receiving a negative rapid antigen result compared to a positive PCR test result.

However, UDOH noted, there has been a nationwide shortage of these more accurate tests, and UDOH’s access to them remains limited.

Concerns first raised last week

Because of those supply chain constraints, Utah began using the GenBody tests in late December, UDOH executive director Nate Checketts said.

State epidemiologist Leisha Nolen added that concerns about the GenBody tests were only raised last week, when some mobile testing partners “noticed that they were getting a lot more negatives that would come up later as positives.”

According to Nolen, for every 100 people who tested positive on a PCR test, only 38% tested positive on the GenBody rapid antigen test. Even for those who displayed clear symptoms of COVID-19, only 41% out of every 100 who tested positive on a PCR test also tested positive on a GenBody rapid test.

“We were really concerned by those numbers, and we certainly want to evaluate why this is happening,” Nolen said.

State testing sites will still conduct PCR testing and offer at-home COVID-19 tests to anyone who receives a PCR test but wants to receive results faster.

People who received a negative rapid test result at a state testing site between Wednesday and Sunday are asked to consider returning to a state testing site to receive a PCR test, UDOH advised.

UDOH noted that the same analysis found positive rapid test results to be “extremely reliable,” so anyone who tested positive on a rapid test should trust that result.

“Really what we were seeing were false negatives, not false positives,” Hofmann said.

Unclear if reliability concerns unique to Utah

Nolen said that UDOH has reached out to partners around the country to determine if they were experiencing similar issues with the GenBody test, and that, so far, “we haven’t heard of any other places” getting similar results.

She said UDOH is working with GenBody and the Food and Drug Administration (which approved the test for usage) to garner additional information and to determine if there is a problem with the test in general, or if there is an issue with how it was being administered in Utah.

Along those lines, UDOH officials were asked Sunday if there was any difference in results among sites run by UDOH mobile test teams, TestUtah and TourHealth that would indicate that there was a problem with how the tests were being administered or used.

Nolen replied that data was examined from both TestUtah and mobile testing teams, and that “it really looks quite similar.” Checketts added that TourHealth had only just begun the process of shifting to the GenBody test, so there was no comparable data available from them.

The excessive negative results also did not appear to be tied directly to the currently prevalent omicron variant of the coronavirus, Nolen said, as a review of the tests conducted in December, when the delta variant was most prominent, yielded similar percentages of negative rapid test results.

Despite supply chain constraints with BinaxNow tests, Checketts said that the state continues to receive a small supply, which are primarily used in higher-risk settings, such as long-term care facilities.

“We just don’t have a sufficient supply right now to do the community testing that we’ve been doing across the state,” Checketts said.

The BinaxNow tests may be reintroduced at Utah testing sites should the state’s supply chain stabilize, he added.