Health: Understanding COVID-19 Testing

By: Alan Pollock

Topics: COVID-19

A pop-up testing clinic was held in Chatham last week.  FILE PHOTO

If you’ve thought about getting tested for the novel coronavirus, you’ve got some challenges to consider, and some homework to do.

There are three general types of tests — molecular, antibody and antigen — and each has advantages and drawbacks. But experts say that for now, there continue to be limits on the availability of tests and the speed with which they provide results.

The gold standard for testing remains the molecular polymerase chain reaction test, known as a PCR.

“That’s the key diagnostic tool for finding out, does somebody have COVID-19 right now,” Barnstable County Health and Environment Director Sean O’Brien said. It’s the PCR test that’s used for pop-up clinics and for the testing facility at Cape Cod Hospital, as well as at Outer Cape Health Services. The process looks for molecular evidence that the virus is present in a swab of saliva or mucus. The PCR is favored because it is highly accurate, but it takes time to get the results.

“We have a few things in play because of the expansion of cases across the rest of the country,” he said. The tests often need to be shipped to labs, and it can take seven or eight days for the results to be reported. From a public health standpoint, that delay is a significant problem. “That test is a diagnostic tool. It’s like a Polaroid for where your body is right now.”

Antibody tests work differently, using a blood sample to check for evidence of a viral infection.

“That will tell you whether you have any coronavirus antibodies in your system,” O’Brien said. The test is useful to determine if a person has been exposed to the virus, but can’t say whether the person is currently infected or is contagious. Results are usually available in a day or two.

In May, the FDA approved the use of an antigen test, which is designed to detect specific proteins that are present on the coronavirus. Antigen tests use a nasal swab, and aim to identify people who have active infections. The tests can be processed in a half-hour, but their reliability can be a problem. Antigen tests pose a risk of false negatives, meaning that they could miss a person who has COVID-19.

“As a screening, it gives some help,” O’Brien said. “But if somebody tests negative and symptoms develop, they’re still going to want to talk to their physician.”

While all three tests are available locally, it’s still largely up to doctors to determine who gets tested, O’Brien said.

“Physicians are still in the driver’s seat,” he said. Candidates for testing are generally people who have symptoms or who have been exposed to someone with COVID-19. The symptoms include a fever, dry cough, flu-like symptoms or the loss of taste or smell. And from a public health point of view, exposure to someone with the virus is more than just passing them on the street.

“Really, they say exposure is over 10 minutes” of being within six feet from another person, O’Brien said.

For those who haven’t been exposed and don’t have symptoms but still want to be tested, the best advice is to wait.

“As much as everybody wants more and more testing to happen, there are still limitations on availability,” he said. And while it seems like we’ve been living with COVID-19 for a long time, it’s still a new virus. “It’s going to take a while for the technology to catch up to it,” O’Brien said. Researchers still don’t know how long antibodies remain in a person after the infection, and how much protection they offer. “A lot of those studies are still happening.”

When it comes to the current high demand for testing, there’s one thing that would likely ease the problem: the availability of a vaccine.

“And so far, things are looking pretty good,” he said. “I think that will take a lot of pressure off of people.”