Mayo Clinic's new test for the virus that causes COVID-19 is described in a recent news release as a PCR test. While most won't know what that means, PCR is a well-used tool in the laboratory and medical testing. Larry Pease, Ph.D., a Mayo Clinic immunologist, and Kyle Rodino, Ph.D., a clinical microbiologist, explain how this test works.
To start, PCR stands for a laboratory technique known as polymerase chain reaction. In this test, the goal is to selectively amplify trace amounts of genetic material, identifying specific parts of DNA. Just as a reminder, DNA is the genetic code that is present in every cell in the body. When a cell divides, it copies DNA, separating the two strands and then creating a new strand of DNA by copying the template. PCR mimics what normally happens in cells.
But why DNA?
DNA is used because at the most discriminating level, the structure of DNA can tell you what organism is being looked at. In the case of humans, PCR can identify a person using his or her genetic signature. In the case of COVID-19, researchers have published more than 100 genomes collected from patients to identify key features of the virus that causes that disease, SARS-CoV-2.
But there's a wrinkle.
PCR only works on DNA, and the COVID-19 virus uses RNA as its genetic code. RNA is similar to DNA, but only has a single strand. Fortunately, viral enzymes to convert RNA into DNA were discovered decades ago, and have been harnessed, along with PCR, to find unique signatures in RNA, too. In this case, PCR is referred to as reverse transcription PCR, or RT-PCR.
This is how it works.
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