Health officials are explaining Ohio Governor Mike DeWine’s differing diagnoses after the governor tested positive and then negative for COVID-19 on the same day.

Dr. Peter Mohler from Ohio State’s Wexner Medical Center explained that DeWine first took an antigen test on Thursday ahead of President Trump’s visit to Ohio, as per White House protocol.

While those results were positive, two subsequent PCR tests both came back negative.

Dr. Mohler says the PCR test is “the gold standard” and much more accurate than the faster antigen tests.