HERSHEY, Pa. — With COVID-19 cases trending upward, it’s important to understand when individuals should get tested and what type of test they should have.
Currently, there are three different types of tests to determine whether someone has COVID-19 or has previously been infected.
PCR
The molecular test, also known as the PCR — short for polymerase chain reaction — is considered to be the most accurate in detecting viral particles. Although samples for the molecular test can be collected from saliva, a nasal swab inserted far back in the nostril — a procedure called a nasopharyngeal swab — remains the preferred way to collect samples.
“The sensitivity of the test is much better when you get that deeper specimen,” said Dr. Catharine Paules, an infectious diseases physician at Penn State Health Milton S. Hershey Medical Center. “Even though it’s uncomfortable, that’s the best way to get the test done.”
Antigen testing
Another way to diagnose COVID-19 is with antigen testing, which identifies viral proteins in a sample, often obtained from a swab of the lower portion of the nostril or from the deeper, nasopharyngeal swab.
“These are more likely to be point-of-care tests performed on plastic card-based assays, similar to a pregnancy test where a line will show up if it’s positive for the virus,” said Dr. Melissa George, interim chair of the Department of Pathology at the Milton S. Hershey Medical Center.
“But right now, only a few antigen tests have received FDA emergency use authorization, and they’re only available in small volumes.”
This method is also not as sensitive as molecular tests.
Antibodies
A third type of test does not look for active infection, but rather for evidence — through antibodies present — that someone has had COVID-19 in the past.
Best test
If someone is concerned that they might have COVID-19, the best type of test is the nasal swab with the molecular testing, explained Paules.
Point-of-care molecular tests that take 15 to 30 minutes to be processed may be available at some physician offices. But because of their lower sensitivity and higher false negative rates, both Paules and George recommend tests that are processed in a laboratory. Physicians can provide patients with lab orders for the test.
Some organizations use molecular tests from saliva samples for surveillance testing efforts. These involve taking a random sample of a percentage of a particular population, such as a university’s student body, in an attempt to identify asymptomatic individuals who might have COVID-19 and could be infectious.
The saliva is collected by spitting in a funnel test tube, usually while a medical provider is watching from a video link to make sure that enough sample is provided.
Presently, the recommendations for when to use antibody tests are limited.
“We’re mostly using them to help us define clinical syndromes that might occur after COVID-19,” Paules said. “For example, multisystem inflammatory syndrome. It’s a serious inflammatory complication of COVID in children. One of the ways that we’ve been able to discover that and diagnose patients with it is through an antibody test.”
As far as considering the results of an antibody test to be a clean bill of health from future COVID infections, Paules advised against that.
Waiting
The turnaround time for test results varies depending on the condition of the person getting tested, George said. While awaiting test results, it’s essential to continue to isolate.
