Share on PinterestThere are two common types of diagnostic tests for the new coronavirus. Experts say both are highly accurate. Getty Images
- Experts say the current diagnostic tests for the new coronavirus are highly accurate while antibody tests are not as trustworthy.
- There are two types of common diagnostic tests — one looks for the coronavirus’ genetic material, while the antigen test searches for proteins.
- Experts say any tests must be done properly to be effective.
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There’s encouraging and not so encouraging news about COVID-19 testing.
The most common tests used to diagnose an infection with the novel coronavirus are almost 100 percent effective if administered correctly.
However, the same can’t be said of tests to determine if you’ve already had the disease and have developed antibodies.
Experts say diagnostic testing is one of the most powerful public health tools for fighting the spread of the coronavirus.
The tests identify people who may need treatment. Results also trace those who have been in contact with other individuals to help prevent the transmission of the disease further. This can assist epidemiologists in determining how widely the virus has spread.
“Testing makes the enemy visible,” said Dr. Emily Volk, an assistant professor of pathology at the University of Texas-Health in San Antonio and president-elect of the College of American Pathologists (CAP).
There are two basic types of tests for the novel coronavirus. One type diagnoses an infection and the other tests for antibodies.
Diagnostic tests detect active infections. This is the test you want if you think you’ve been exposed to the coronavirus or are exhibiting symptoms of COVID-19.
There are currently two types of diagnostic tests available.
- The molecular real-time polymerase chain reaction (RT-PCR) test detects the virus’s genetic material.
- The antigen test detects specific proteins on the surface of the virus.
The RT-PCR nasopharyngeal tests are more widely used and more familiar. Most involve sticking a 6-inch swab deep into your nose to collect virus samples to test.
However, some more recently approved RT-PCR tests seek to avoid the discomfort associated with the nasopharyngeal swab tests by allowing samples to be collected via a shallow swab of the nose or by testing saliva for the presence of the virus.
If performed correctly, RT-PCR swab tests “would be pretty close to 100 percent accurate,” Volk told Healthline.
“We should be diagnosing people with PCR tests because they are the most accurate,” added Dr. Christina Wojewoda, a pathologist at the University of Vermont and vice chair of CAP’s microbiology committee.
To get the most accurate results, RT-PCR tests should be conducted 8 days after suspected exposure or infection, to ensure that enough viral material is present to detect.
“Some clinicians know that, but people who are swabbing may not be passing that information along,” Wojewoda told Healthline.
It’s also possible to administer the test too late, after the body has successfully fought off the disease, according to Dr. William Schaffner, professor of medicine in the division of infectious diseases at the Vanderbilt University School of Medicine in Tennessee and medical director of the National Foundation for Infectious Diseases.
The test must also be administered properly, which means inserting the swab 3 inches or so to reach the cavity where the nasal passages meet the pharynx.
“If you’ve had this test and it wasn’t uncomfortable, it wasn’t done correctly,” Schaffner told Healthline.
False-positive results, while rare, can occur with PCR tests, said Wojewoda, because the coronavirus’ genetic material may linger in the body long after recovery from an infection.
“You can’t tell if the person [had an infection] 3 days ago or 5 months ago,” she said.
Swabs are also used to collect samples for antigen testing. These tests have the advantage of yielding faster results (hours rather than several days).
They’re also less accurate than RT-PRC tests, mostly because they require test samples to contain large amounts of virus proteins to yield a positive result.
False-negative results from antigen tests may range as high as 20 to 30 percent.