Ohio Gov. Mike DeWine tested positive, then negative for COVID. 7 questions you might have about testing. – USA TODAY

At-home testing could transform the fight against the novel coronavirus. USA TODAY

Ohio Gov. Mike DeWine tested positive for COVID-19Thursday using a rapid test conducted as part of protocol to greet President Donald Trump at Clevelands Burke Lakefront Airport.

TwoPCR teststaken later that day ultimately found DeWine tested negative.

"This is the same PCR test that has been used over 1.6 million times in Ohio by hospitals and labs all over the state, DeWine said in a released statement soon after the second tests results were released.

DeWines COVID scare underscores the fact thatnot all tests work the same way, nor do they alwaysprovide identical results. Even the same testtaken twicecan show contradictory outcomes.

"It's not that a test is good or bad," explained Dr.Dr. Gary Procop, the director of medical microbiology at theCleveland Clinic."Understand the test characteristics and use it correctly."

Dr. Michael Mina, an infectious disease epidemiologist at the Harvard T.H. Chan School of Public Health, saidDeWine's ability to quickly get asecond test showed "the system worked as it should."

Every test sometimes gives false positives which is better than telling someone they don't have COVID-19 when they do and being able to get a new result within a few hours meant he was inconveniencedonly briefly. "It's a whole lot better than if we weren't testing him at all and he were positive."

Here are answers to seven common questions about diagnostic COVID-19 testing. These tests are different thanantibody tests, which are usedto determine whether someone has had COVID-19 in the past not an active case.

Earlier: Ohio Gov. Mike DeWine tests negative on second COVID-19 test

USA TODAY Editorial Board: Time to get serious about COVID-19 testing

A rapid test, explained Dr. Sheldon Campbell, aprofessor of laboratory medicine at Yale School of Medicine, is a catch-all term for any quick test. Any test that provides results in 30 minutes to one hour, he said, falls under the umbrella of rapid testing.

"Seriously, its not a specific technical term," he told USA TODAY.

In rapid testing, explained Procop, there are two kinds of tests antigen tests and nucleic acid tests.

An antigen test, Campbell said,looks for the proteins that make up the virus coating.

Think of the virus like an M&M, Campbell suggests. Antigen tests look for traces of the hard-shell exterior of the virus, so to speak.

While they provide results more rapidly, they are not a perfect test. The Food and Drug Administration states that antigen tests are more likely to miss active coronavirus infections, and thus, cannot definitively rule out whether someone has COVID-19. DeWine's first test was an antigen test.

A PCR (polymerase chain reaction) test searches for the viral genome.This test, explained Campbell, makesthe virus easier to detect by "making a billion copies of a single target bit of the virus genome."

To go back to the M&M analogy, Campbell likens the viral genome to the chocolate core of the candy.

These tests are more commonand have a higher rate of accuracy.

Here's where things get a bit tricky. Generally, PCR tests tend to be more reliable.

"Its both more likely to detect the SARS-CoV-2 virus and usuallyless likely to give a positive signal if no virus is present," said Campbell.

But Procop says the type of test is less relevant than the context in which it is performed. In a screening context, a patient generally wouldn't have symptoms of COVID-19, whereas in a diagnostic setting, patients get tested because they show symptoms.

"If you're using a highly sensitive test in a diagnostic setting," he said,"you don't need follow up. If you use it in a screening setting, you should have confirmation."

Essentially, if you're taking a test out of an abundance of caution and don't show any symptoms it's worth taking another one in the case of a false positive.

The super-short answer, joked Campbell, is that "(expletive) always happens." Anumber of factors contribute to the possibility that any lab test could result in incorrect outcomes.

Each test provides its own slew oferrors.

Antigen tests get false results because its procedure requires "sticking a labeled probe to the virus proteins."

"Despite the best efforts of the people who design the tests, sometimes the probe sticks to non-virus sticky stuff in the sample," Campbellsaid.

For PCR tests, the same sensitivity that contributesto its accuracy can create false positives. Abit of viral RNA from a previous patient can turn a testpositive.

There are also human errors that come into play, whether lab specimens improperly collected or labeled, or manufacturing errors with testing kits.

Absolutely. It remains unclear why that is, Campbell said, but a common theory he suggested is that "bits of non-infectious virus" slowly work their way out of the body even after symptoms have vanished.

"Some folks with COVID-19 stay positive for days or weeks after they get better," Campbell said.

That's also why the U.S. Centers for Disease Control and Prevention, explained Procop, changed its criteria for employees returning back to work,from two weeks to 10 days after a positive test.

"There'sa long tail of positivity after patients have recovered and we believe it's clinically meaningless," he said.

Expect the long swab. There are different nasal swabs with varying degrees of efficacy.

The long swab, otherwise known as the nasopharyngeal swab, is probably the bestand is most common if you do demonstrate symptoms of COVID-19.

An alternative is thenasal mid-turbinateswaband a less-invasive "anterior nares"swab, which are less effective but sufficient.

Still, the long swab is the gold standard. Campbell puts it this way: "The swab goes farther up your nose than maybe you thought it should, and done right it burns when its up there.But its over quickly, and feeling the burn means you know your test was done right."

Follow Joshua Bote on Twitter: @joshua_bote.

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Ohio Gov. Mike DeWine tested positive, then negative for COVID. 7 questions you might have about testing. - USA TODAY