How accurate are coronavirus diagnostics and antibody tests?

Diagnostic tests detect active infections. This is the test to do if you are exposed to coronavirus or if you think you are showing symptoms of COVID-19.

There are two types of diagnostic tests currently available.

• The molecular real-time polymerase chain reaction (RT-PCR) test detects viral genetic material.
• Antigen tests detect specific proteins on the surface of the virus.

The RT-PCR nasopharyngeal test is more widely used and more familiar. In most cases, a 6-inch swab is pierced deep into the nose and a sample of the virus is taken and tested.

However, some recently approved RT-PCR tests either allow samples to be collected through a shallow-nosed swab or by testing saliva for the presence of the virus, which results in the non-pharyngeal swab test related problems. Trying to avoid pleasure.

If done correctly, the RT-PCR swab test “will be pretty close to 100% accurate,” Volk told Healthline.

“The PCR test is the most accurate and should be diagnosed,” he added. Dr. Christina Voivod, A pathologist at the University of Vermont and vice-chairman of the CAP Microbiology Committee.

For the most accurate results, RT-PCR tests should be performed 8 days after suspected exposure or infection to ensure that sufficient viral material is present to detect.

“Some clinicians know that, but the person who is swabing may not have given that information,” Wojewoda told Healthline.

According to it is also possible to delay the test after the body successfully overcomes the disease Dr. William Schaffner, Dean of Medicine and Dean of Infectious Diseases at Vanderbilt University of Tennessee National Infectious Disease Foundation..

Also, the tests should be conducted properly. That is, insert a swab about 3 inches until the nasal cavity reaches the cavity that meets the pharynx.

“If you didn’t feel uncomfortable with this test, it wasn’t done right,” Schaffner told Healthline.

False-positive results are rare, because coronavirus genetic material can remain in the body long after the infection has recovered, but it can occur in PCR tests, Wojewoda said.

“That person [had an infection] 3 days or 5 months ago,” she said.

Swabs are also used to take samples for antigen testing. These tests have the advantage of delivering faster results (hours instead of days).

It is also less accurate than the RT-PRC test. This is mainly due to the large amount of viral proteins that must be included in the test sample to get a positive result.

False-negative results from antigen testing can range from 20% to 30%.

“If you have a positive antigen test, you can believe it,” Wojewoda said. “If it’s negative, you have to doubt it.”

As the name implies, these tests look for antibodies produced by the immune system in response to new coronavirus infections.

Antibody tests are not diagnostic tests.

“Antibodies can take days to weeks after infection, and can stay in the blood for weeks after recovery.” Food and Drug Administration (FDA).. “For this reason, antibody testing should not be used to diagnose active coronavirus infections.”

Antibody tests are also not very useful.

Ideally, a positive antibody test shows recovery from COVID-19 or coronavirus infections, showing immunity to future infections, work, without the risk of transmitting the infection or getting sick. Travel and go back to society. Again yourself.

But researchers still don’t know if the presence of antibodies means that they have immunity, if they can get sick with another viral strain, or how long the immunity lasts. Hmm.

“There is a problem because antibody testing can be easily misused,” says Volk. “If you have a positive antibody test that doesn’t require you to wear a mask or adapt to social distances, the antibodies let us know that you have immunological protection against future infections. not.”

Antibody tests are also subject to false positive results.

“Antibody’s job is to stick to things and produce positive test results when reacting to different types of coronaviruses,” Wojewoda said.

“Antibody tests are most promising if the way the human body controls coronavirus is through antibody responses,” Wojewoda added. “If not, it makes no difference.”

For example, it’s T cells, not antibodies, that help the body fight HIV infection, she said.

“This is another piece of data that we need to understand before we understand testing,” says Wojewoda.

All COVID-19 tests currently (and legally) available in the US have been approved by the FDA under FDA approval Emergency use permit (EUA) protocol.

The EUA states that the FDA “uses unapproved medical products or unapproved use of approved medical products in emergencies to identify serious or life-threatening causes caused by chemical, biological, radiation, and nuclear threat agents. Allows to diagnose, treat, or prevent a disease or condition associated with illness.There is no suitable, approved, and available alternative.”

This allowed us to bring new coronavirus tests to market quickly, without the research and testing normally required for FDA approval.

To date, the FDA has approved 130 different RT-PCR, antigen, and antibody tests for the new coronavirus.

“It takes a long time to do a full clinical trial, but now we need testing,” he said. Dr. Shelley Dunbar, Senior Director of Global Scientific Operations, Luminex Corporation. Produced a pair of PRC tests and submitted an application to the FDA for emergency approval of a new antigen test.

Experts generally agree that RT-PCR tests are more accurate and useful than antigen and antibody tests, which are better used as confirmation tools.

Dunbar told Healthline that some test labs use multiple tests to predict shortages of test products. We also use faster tests when demand is high, and slower and more accurate tests on weekends or later hours.

Wojewoda said that while some tests promise faster results than others, the biggest limiting factor in improving results is the lack of reagents, the chemicals used in the tests.

“I’m not looking for a new test,” she said. “What’s on the market is as accurate and fast as you need it. You have some equipment that needs to be tested. There is more you need to do that.”

Like most of the new coronaviruses, pathologists and laboratories are learning about COVID-19 on the spot, Dunbar said.

“In my career, I’ve never seen anything like researchers and the public discussing and analyzing data,” she said. “We respond based on our past knowledge of other viruses, but I would like to say that bugs do not read books. What happened in the past helps prepare, but things have evolved. continue.”