Differences between rapid tests and standard tests for COVID-19

Ask the Expert

GREENVILLE, S.C. (WSPA) – The Centers for Disease Control’s latest guidelines said that if you have been in close contact with someone who is positive with COVID-19, you should quarantine immediately for at least 7 days and wait 5 days before getting tested.

The CDC defines “close contact” as having done any of the following:

  • You were within 6 feet of someone who has COVID-19 for a total of 15 minutes or more
  • You provided care at home to someone who is sick with COVID-19
  • You had direct physical contact with the person (hugged or kissed them)
  • You shared eating or drinking utensils
  • They sneezed, coughed, or somehow got respiratory droplets on you

Bon Secours’ Dr. Dawn Zellner said she has been getting many questions from patients about the reliability of rapid tests and the difference between that and the standard nose swab test. She said the standard nose swab test for COVID-19 is called the PCR test, short for polymerise chain reaction test, and is considered the “gold standard” in SARS-CoV-2 detection.

“We have to send it to specialized labs,” she said. “That turnaround time can take anywhere from a day to 7 days, depending on how many tests the labs have and how backed up they are.”

On the other hand, she said the rapid test that Bon Secours uses, made by Abbott, can show results within 15 minutes, but is less sensitive to the virus.

“The manufacturer says that test is about 95 percent sensitive and specific. That’s a good test, but that’s within the first 7 days of symptoms,” she said. “If it’s positive, you have contagious disease. If it’s negative, we have to send off the PCR to see if you have the disease.”

As of December 2nd, the CDC said that if you have been exposed to someone with the virus with no symptoms, you should quarantine for 10 days. If you have no symptoms and get tested, it recommended getting tested 5 to 7 days after exposure, and with a negative result, said quarantine can end on day 7.

After ending quarantine, it said to watch for symptoms until 14 days after exposure. If you have symptoms, it said to immediately self-isolate and contact your local public health authority or healthcare provider.

Dr. Zellner explained that waiting for 5-7 days from exposure before testing will allow the virus to become detectable while you are contagious. “Typically you’re going to have symptoms within the first 5 days on average, but it can be up to 14 days.”

Still, if you take a rapid test and receive a negative result, Dr. Zellner cautions that you are not necessarily in the clear and could still be contagious.

“If you do have the virus, but its a very low amount and it’s taking a long time to sort of replicate itself and build up in our system, then our rapid test is not going to work.”

That is why the rapid test is most useful if you are showing symptoms, she said, to confirm if you are positive.

“If you are sick and you have fever and cough and you’ve had 2 days of it, we can do a rapid test and we can say yes you have COVID-19 and need to go home and stay home for 10 days since the onset of symptoms.”

For a list of COVID-19 symptoms and more information about testing, click here.

If you have a health topic for our series, click here.

Copyright 2021 Nexstar Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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