Rapid antigen tests helping drive increase in NC COVID testing numbers

North Carolina news

RALEIGH, N.C. (WNCN) — Rapid antigen tests account for a growing share of the COVID-19 testing numbers in North Carolina.

The state is processing nearly three times as many antigen tests as it did a month ago — an average of 2,000 of them each day over the past week.

During that same time frame, the seven-day average number of the slower, more expensive PCR tests has only grown by 17 percent, with that figure at 35,626 on Wednesday.

Overall, the average number of tests has increased by more than 20 percent over the past month. The state averaged 37,626 tests processed per day during the past week.

The state Department of Health and Human Services only started reporting those antigen tests along with those counts in late September.

In all, antigen tests account for just over 1 percent — about 55,000 — of the 4.4 million tests processed so far by the state. But they have caught 4.5 percent of the more than 300,000 confirmed cases of COVID-19 the state has recorded since March.

And that percentage varies wildly on individual days — for example, antigen tests accounted for two thirds of the cases confirmed so far from specimens taken Tuesday. 

There is often a lag of a few days between when a specimen is collected, a case is confirmed and when it is added to the daily total.

Increased testing is considered a key component of the COVID-19 response because it allows for infected people to isolate before they can further spread the virus to others.

“I think we’re getting better all the time,” said Tom Denny, a professor of medicine at Duke University and an expert on testing.

“Having said that, I think we can still make incremental improvements in areas, and we have a long way until we get this … pandemic under control and I’m a believer that testing helps us do that. And so the more we can test, I think the better off we’re going to be.”

Both main types of tests have pros and cons. 

Rapid antigen tests are less expensive, can be conducted in point-of-care facilities and produce results faster — in a matter of minutes, compared to the average 2-day wait for results from a PCR test. While PCR tests look for the virus’ genetic material, antigen tests detect specific proteins from the virus.

And antigen tests are most effective at detecting COVID-19 when a person has a high viral count, Denny said.

The FDA recently warned clinical laboratory staff and health care providers of the possibility of antigen tests producing false positives at a higher rate, but Denny says that’s not as serious of a concern as it might sound.

“It’s a balance in general. I think I’d rather have some false positives, test more, have a larger cohort of people that are able to be tested, screened out,” he aid. “And then if I have to go on to confirm in another testing platform, I’d rather do that, than not have access to testing.”

The general consensus among experts is, the more testing, the better, but it’s hard to put a firm number on that.

Researchers at the Duke-Margolis Center for Health Policy say that while fewer than 25 million tests are being reported monthly across the country, that number could rise to nearly 200 million each month by January with point-of-care tests making up about 70 million of those. The researchers are calling for federal guidance, funding and coordination with state and local governments.

Denny says Duke’s aggressive testing policy of asymptomatic people across campus is a major reason why the school has remained open throughout the semester.

“I’m not a public health expert who would do the modeling for that but I would say we could double or triple the testing we’re doing today, and if we could do that, we could really see some changes in the trajectory lines,” Denny said. “We’d be able to identify those infections, put people in isolation and prevent that from seeding new infections.”

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