New rapid antigen tests come with their own positives and negatives
With greater speed comes a greater potential for error.
By Conor Johnson / The Blade
Tue, 11 Aug 2020 18:57:20 GMT
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A rapid new type of coronavirus test may be coming to Ohio soon, and with it comes new benefits and drawbacks.
Gov. Mike DeWine announced Aug. 4 a bipartisan effort with six other states and the Rockefeller Foundation to purchase 3.5 million rapid antigen tests, the first multi-state coordinated testing strategy.
These tests are able to deliver results at a much faster pace than current diagnostic tests. But with this speed comes a greater potential for error – the most prominent example of which was Gov. DeWine’s false positive test on Thursday.
“Every type of test has its pluses and minuses,” Toledo-Lucas County Health Commissioner Eric Zgodzinski explained. “Each test is only as good as what it’s meant to do.”
Broadly speaking, coronavirus testing can be split into three types. Almost all of the testing done in Ohio so far has been polymerase chain reaction tests, which take a sample from a person and attempt to amplify portions of the coronavirus’s genetic code. These highly sensitive tests should detect very low amounts of virus from currently infected people, said Lauren Wagener, the county health department’s epidemiologist.
The process of amplification and analysis for a sample takes a few hours, however, meaning the test turnaround time can be “12 hours if you’re lucky and up to seven days if you’re unlucky,” Ms. Wagener said.
A surge in demand for PCR tests combined with their slow speed has created backlogs in Ohio and elsewhere, hurting health departments’ efforts to track the virus and warn others of potential exposure.
Antigen testing, on the other hand, is the hare of the testing world — taking as little as 15-20 minutes for results from a mouth or nose swab. Instead of PCR amplification, antigen tests quickly detect specific proteins on the surface of the coronavirus.
In fact, almost everyone has encountered other antigen tests before when getting quick swabs for flu or strep throat during routine doctor’s visits.
The third broad category is antibody testing, which determines whether a person has been previously infected. These tests use a blood sample to check for defensive antibodies against the virus.
Ms. Wagener and Mr. Zgodzinski agreed that antigen testing’s speed would allow for more timely contact tracing efforts, reducing the disease’s spread.
“These types of tests are good because we’re able to quickly identify cases of COVID,” Ms. Wagener said. “It doesn’t help us to inform contacts in an appropriate amount of time to quarantine when we’re waiting seven or more days to get a result back.”
Antigen testing’s downside is less accurate results, such as Governor DeWine’s. His positive antigen test was later overruled by two separate negative PCR tests.
But the governor’s false positive was exceptional. By their nature, antigen tests “are more likely to miss an active coronavirus infection compared to molecular tests,” according to the U.S. Food and Drug Administration’s website. Because they do not amplify portions of the virus like PCR tests, there is less to latch onto, possibly resulting in a negative result for someone currently infected.
Ms. Wagener acknowledged antigen tests are less reliable and encouraged anyone unsure of test results to follow up with a primary care physician and possibly get a PCR test as well.
Still, local public health experts said that despite the occasional wrong result, these tests could provide a powerful new tool in the fight against the coronavirus. Professor Joseph Dake, who chairs the University of Toledo’s school of population health, noted that no test is perfectly accurate.
“You never want to have perfect be the enemy of effective,” he said.