Different types of COVID-19 tests explained

News Connection

There are three types of tests available for COVID-19

SAN ANGELO, Texas — Health officials say even with the numbers of people being tested in San Angelo for Coronavirus, those in the area who are actually infected with COVID-19 is likely to be five to ten times higher.

“We think it’s very important to give accurate numbers to the public,” said Chris Barnett, MD, Chief Medical Officer for Shannon Medical Center.

There are three types of tests available for COVID-19: polymerase chain reaction (PCR), antigen, and antibody (serology) testing.

Both PCR and antigen tests determine if a person has an active infection of the virus by collecting a nasal swab.

“Both the PCR and the antigen tests are very accurate, meaning if it says you are positive, there’s a very high likelihood that is correct,” added Dr. Barnett.

According to Dr. Barnett, a negative PCR test means that a person was likely not infected with the virus.

“The PCR test is done through a nasal swab. It takes a sample of mucus from the nasal passage and it’s testing for genetic material within the virus. That test takes a small amount of genetic material and amplifies it to a much larger number so that it can be readily seen in the test,” explained Dr. Barnett.

However, a negative antigen test does not rule out COVID-19.

“The antigen test is similar to the PCR test in that it is looking for certain parts of the virus, primarily proteins that are on the outside of the virus. However, that test is not able to amplify the viral particles. If there are not enough present in the sample, it will not show a positive result,” continued Dr. Barnett, “That means you don’t have enough virus on the sample for the test to pick up and show a positive result. That may be because it’s too early in the process or it may be that the virus is not there in enough numbers to show up as a positive result.”

While PCR tests are the more reliable of the two, they are in limited supply and have to be sent out to labs with a current turnaround time of 24-48 hours. Antigen tests can be done rapidly and in-house, in 15 minutes or less. At the Shannon drive-through testing sites, half the people who arrive for COVID-19 testing are given PCR tests, and the other half antigen tests.

Another type of COVID-19 test is an antibody test. It takes a blood sample to determine if a person was previously infected by the virus, so they can donate plasma to treat other patients with COVID-19.

Even with all the testing being done, Dr. Barnett says the number of positive cases reported every day does not accurately reflect the number of people who are infected because of the small percentage of the population that is being tested.

“We know that if anything, the numbers are low. Five to ten times as many people actually have the virus as those who are getting tested,” explained Dr. Barnett, “For people who feel that the numbers are over-reported, it’s actually the other way around. A lot of people do not get tested and go through this illness with minimal or no symptoms. If everyone is tested, we would see much higher numbers.”

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Current status of COVID-19 testing in San Angelo