What causes differences in coronavirus testing results?

Posted at 9:32 AM, Oct 02, 2020
and last updated 2020-10-02 09:32:29-04

LEXINGTON, Ky. (LEX 18) — Since the COVID-19 pandemic began, there's been a lot of research done on the virus and advances in testing. However, depending on where you go, the way you're tested, and how long it takes to get results differ.

“We are learning as we go. There really have been rapid shifts in terms of what's the best way we can take care of people in the state of Kentucky and around the world,” said Zach Porterfield, an assistant professor of medicine at the University of Kentucky with focuses on microbiology, immunology, infectious disease and ENT surgery.

Depending on where you get tested, results can vary. While one person may get results back within a few hours, it could take up to a week for someone else. Porterfield says there are several factors, like the type of test you take.

“One of them is a PCR-based test, one of them is an antigen test and one is an antibody test,” he said. “The PCR tests and the antigen tests test for presence of virus at this moment. We can talk a little bit about PCR being a more sensitive test, but does take a little bit longer to run and an antigen test maybe being less sensitive, but can often be run a little more quickly.”

Those two tests include the nasal swabs and PCR tests are more commonly found right now. Other factors include where you're located and what resources are available to labs to test samples. More resources can mean a quicker turnaround.

Then there’s the concern of getting the right result. Porterfield says there is a higher chance of false negatives with PCR tests; anywhere from 2 to 5% or even up to 35% in some cases. His advice is while it may be uncomfortable, make sure you're performing the nasal swab correctly to get the proper sample. Also, if you think you've been exposed to the virus, wait a bit to get tested.

“If I have an exposure today and I test today, it's very unlikely that any test will be positive and that doesn't mean that I'm free,” said Porterfield. “Waiting a couple of days, four, five, six, seven days, before getting that test increases the chance that that test is going to be accurate.”

For anyone who has had COVID-19, getting an antibody test helps with ongoing research on how the virus affects people.