Ohio Gov. Mike DeWine tested positive for COVID-19 on Thursday before testing negative later in the day using a different test.
He was tested because he was scheduled to meet with President Donald Trump during his visit to Ohio.
Test results can be affected by a variety of factors, including the type of test used, the quality of the sample and when it was taken during the course of any infection.
DeWine initially received an antigen test, a type of rapid test that uses technology similar to screenings for flu, strep throat and other infections.
Instead of detecting the virus itself, such tests look for proteins, or antigens, found on the surface of the virus. The test, which uses a nasal swab, takes about 15 minutes.
The tests are relatively new in the U.S. and federal regulators have only allowed two on the market, from manufacturers Quidel and Becton Dickinson.
A DeWine spokesman said a Quidel test was used for DeWine; a spokesman for Quidel said the company is looking into the matter.
Antigen tests may deliver false negatives, missing real COVID-19 infections.
They are considered very accurate for ruling out the virus when it is not present, making false positive results unlikely — but not impossible.
Some experts have been calling for increased use of antigen tests because they can be developed quickly, avoiding the delayed results frequently seen with higher-grade tests that must be shipped to a laboratory for processing.
After testing positive with the antigen test, DeWine said he and his wife received a genetic test that came back negative. This is the most commonly used test in the U.S. and is considered the most accurate.
These tests take several hours to process and are done at large laboratories, hospitals or universities.
A third type of test uses technology similar to the genetic test but speeds up the process dramatically to deliver results in about 15 minutes.
These tests done on small machines are used at the White House and at nursing homes to rapidly screen for the virus.
But federal regulators consider them slightly less sensitive than the conventional laboratory test.
Even the most accurate genetic test usually only begins detecting the virus three to five days after initial infection, when levels are high enough to be picked up.
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