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Understanding pros and cons of COVID-19 tests

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With the presence of rapid or quick COVID-19 tests in the area, there are new questions about the types of tests that are available and which is most reliable. According to Dr. Philip Fracica, Bothwell Regional Health Center’s chief medical officer, the answer depends on the type of test.

“There are generally two ways to detect a virus,” Fracica said. “We can look for an active virus, or we can look for evidence that the body has already had the virus.” 

For people with a suspected active case of COVID-19, there are two tests, molecular and antigen. Molecular tests look for the virus’s genetic makeup or “fingerprint” in a nose or throat swab or saliva samples. The most common is a polymerase chain reaction (PCR) test. Results from standard PCR tests are usually analyzed in a lab and are nearly 100% accurate.

Bothwell uses the standard PCR test and sends specimens to its in-house lab for results, which take 12-24 hours. When more than 300 tests in one day are performed, additional tests are sent to Quest Diagnostics, an external lab, and results take about three days. As of Oct. 15, nearly 26,000 tests have been performed by Bothwell and Katy Trail Community Health. 

Antigen tests look for specific proteins on the surface of the virus, Fracica said. They are sometimes referred to as rapid diagnostic tests because it can take less than an hour to get the test results. They are becoming more widely available because they are easy, simple and inexpensive. 

“The rapid tests perform best when a person is in the early stages of the infection when the viral load is high,” he said. “A positive result is likely reliable; however, a negative test should be analyzed together with the person’s exposure history and symptoms and followed up with a standard PCR test if needed.”

There are rapid PCR tests available as well, including a rapid PCR available at Bothwell. Although this is not an antigen test, this particular assay also is less sensitive than standard method PCR testing.

To determine if someone has already had the virus, an antibody test is used. Antibody tests are blood tests that look for signs that a person has had an infection with the virus and had an immune response. 

“Antibodies generally develop gradually over weeks following a new infection,” Fracica said. “They fit viral proteins like a key fits a lock, and we can test a person’s blood to detect them.”

Fracica said that antibody tests shouldn’t be used to detect a current infection and that caution should be exercised with rapid tests.

“While they are appealing because they decrease the amount of time someone has to wait for results or be isolated, a negative result from a rapid test could provide a false sense of security since there’s a high false-negative rate if tested at the wrong time,” he said. “It’s important to ask for the more reliable standard PCR test to be certain.”

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