Doctors weigh in on accuracy of PCR, rapid antigen Covid-19 tests

MILWAUKEE (CBS 58) -- New questions are arising about COVID-19 tests as the home tests become more accessible.

Some people have heard swabbing your throat instead of your nose may give you a more accurate answer.

"Swabbing your throat first and then your nose is what other countries have done, and I can tell you for myself, personally, that's what I did," Dr. David Letzer said.

Dr. David Letzer is on the Wisconsin Medical Society COVID-19 Task Force. He said although these tests are not approved by the FDA to be used in the throat, preliminary studies show the viral load with omicron is higher in the throat and mouth at first. He recommends using the same swab to swab your throat first and then your nose.

"Unofficially I would say if you have symptoms and rapid antigen is positive on your throat, it's probably real," he said. "With any pandemic, information is ever-changing and that's what -- preliminarily -- is what we think is going on."

Last week, CBS 58 reporter Melissa Zygowicz took both a rapid antigen test and PCR at the same time. The rapid test came back positive, the PCR came back negative. What happened here, and which test should she trust?

"My brother had the exact same situation, I cannot give you a good reason. If you're having symptoms and your rapid antigen is positive, I'd probably run with that," Dr. Letzer said.

Dr. Hashim Zaibak, a pharmacist at Hayat Pharmacy, said in this case, Melissa potentially did not go deep enough in the nose with the PCR test. False positives are extremely rare.

"They may not get the right sample and that can create a false negative," Dr. Zaibak said.

So, how do you make sure you get an accurate result if you're swabbing yourself?

"Five seconds in each nostril and twist, go deep, but you don't have to go as deep as we used to," Dr. Zaibak said.

To get the most accurate test, Hashim recommends having the person at the testing site swab you instead.

"But some people just tell us I don't feel comfortable having someone else doing it for me, I'll do it, and then we watch if they're doing it properly," Dr. Zaibak said.

Dr. Zaibak said both the antigen and PCR tests pick up the omicron variant just as well as the previous variants.