How a positive became a negative: Decoding differences in diagnostic tests

Most of the time, when a politician flip-flops, it’s roundly criticized. But when Ohio Governor Mike DeWine recently went from having COVID-19 to a declaration of health—all within a few hours, it attracted more questions than critique.

How can a COVID-19 test find the leader of Ohio ill in the morning, and prevent him from meeting President Trump during a visit to Cleveland, and give him the all-clear in the afternoon?

The answer, it seems, lies in the nature of the test.

The Food and Drug Administration has approved two types of diagnostic tests to determine if a person has an active coronavirus infection: antigen and molecular tests.

Antigen tests are faster, less expensive and less accurate than molecular. You can get results in minutes. They can be the wrong result, but hey, at least it’s quick!

The test uses a nasal or throat swab to capture a sample of proteins that are part of the COVID-19 virus. The first test DeWine took was an antigen test at a mobile testing site in a parking lot, which is part of a standard protocol for anyone who will interact with the president. Antigen tests are often used to screen large groups of people quickly. However, they can produce false negatives, meaning that people with COVID can be left to walk among the healthy, and false positives, like DeWine received.

The second test administered to DeWine was a molecular test, also known as a polymerase chain reaction (PCR) test. When you take a PCR test, it detects the virus' genetic material and the results are highly accurate. A health care worker collects fluid with a nasal or throat swab, and your sample is sent to a laboratory for results. Considered to be the gold standard with greater than 98% accuracy, a PCR test can detect even the smallest presence of the virus. PCR tests also have high "specificity," which means they return fewer false negatives than antigen tests. DeWine’s PCR test samples were run by Ohio State University’s Wexner Medical Center lab.

Oberlin is using PCR tests to gauge the health of all faculty, staff, and students. Everyone will be tested in August and each month thereafter. We are partnering with an outside lab in Chicago to ensure accuracy.

You may have heard about a third test, which measures antibodies to indicate whether the virus has infected a person in the past. The test involves a blood draw, and results are generally available within three days. These tests only detect antibodies the immune system develops in response to the virus, not the virus itself, and should not be used to diagnose an active infection. It can take days to several weeks to develop enough antibodies to be detected in a test.

So don’t let DeWine’s COVID flip-flop shake your confidence in the PCR tests Oberlin has ordered. Remember, not all swabs are created equal! Our tests are nearly flawless. Obies are being tested by the most accurate swabs of all!