Two Tests, Two Results: Explaining Gov. DeWine's COVID Testing Confusion
Gov. Mike DeWine's coronavirus testing experience this week – in which he came back positive for COVID-19 in one test then negative in a second test just hours later – has caused a lot of questions surrounding the reliability and accuracy of testing.
DeWine's initial positive result came from a rapid-result antigen test Thursday morning, as part of the protocol to greet President Donald Trump during his visit to Ohio. The test was arranged by the Republican National Committee at a mobile testing site at Case Western Reserve University.
An antigen test detects certain proteins that are part of the COVID-19 virus. These tests can be tricky to get right, says Dr. Gigi Grovall of Johns Hopkins University.
“The challenge is, with the rapid antigen test, they might be too easy to mess up on the lab side,” Grovall says. “They have very specific storage needs. You have to read the test within 15 minutes or it's not valid.”
False negatives with the antigen test are common: In one study, 20% of positive COVID-19 cases were missed.
But according to the FDA, positive results are usually highly accurate. That’s why Grovall believes there may have been a lab error.
“If there’s a failure in that kind of test, the failure is usually that it doesn’t pick it up, that it’s not sensitive enough,” Grovall says. “The way that the test works, it’s a little bit rarer to have a false positive, like what the governor had.”
In a statement Thursday, DeWine's office says Ohio doesn’t have a lot of “experience” with the rapid antigen tests, which may have contributed to the false positive.
Or, there may be an issue with the test itself. What happened to DeWine also happened to residents in a town in Vermont. There, 65 people took an antigen test from Quidel, the same company that did DeWine's test. They all tested positive.
However, after taking follow-up PCR tests, the majority of those Vermont residents tested negative, just like DeWine. Quidel could not be reached for comment.
When he came back to Columbus on Thursday afternoon, DeWine also did a PCR test, which is more sensitive and accurate. The PCR test detects genetic material of the virus using a lab technique.
There are several different PCR tests available, says Linda Garner of CAS, a division of the American Chemical Society.
“There are a number of tests that different manufacturers have created, that are this PCR type of test,” Garner says. “And they’re all a little bit different. They use different reagents, and they use different tests or platforms to actually run the test.”
Tests on samples from DeWine were run on different diagnostic platforms at Ohio State’s Wexner Medical Center.
Wexner Medical Center is responsible for about 10% of the state's total coronavirus testing, and they test more than 1,000 patients per day in Columbus. Unlike the rapid antigen tests, labs have a lot of practice with the PCR tests.
DeWine will take another PCR test this weekend. It is generally recommended that people wait five days from possible exposure before getting a PCR test, to have the best chance of receiving accurate results.