By: Zeynep Tokuz
On March 19th, 2020, Governor Gavin Newsom issued the stay-at-home order forcing millions of Californians to shelter in place. Nearly all shops were closed. Major events were canceled. No one was allowed outside. The reason for all this? The coronavirus outbreak.
Since then, many technological advancements have helped us learn more about the virus. You might have heard certain terms emerge such as antigen testing, mRNA vaccines, or PCR, and you might wonder: what do these scientific terms mean? Today, we’ll be discussing PCR testing and, more specifically, how it works.
What is PCR Testing?
PCR is an acronym for polymerase chain reaction (also known as molecular photocopying) and was invented in the 1980s; it helped scientists identify and diagnose genetic defects and detect viruses in human cells. You might have heard the phrase “PCR testing” recently, which is a form of testing used to identify whether or not the coronavirus has been contracted. For a PCR test to function, scientists take a sample of blood, saliva, mucus, or tissue and run it through a special machine which then tests for the presence of the virus or pathogen. Today, healthcare workers use nasal swabs to acquire samples from anyone who requires a COVID-19 test.
How does a PCR Test work?
Upon acquiring the sample of DNA from the subject, healthcare workers perform PCR in a thermal cycler, which acts as a copy machine by amplifying a specific genetic sequence for 20-30 cycles. After an hour, billions of copies of the DNA are be synthesized. The large quantity of DNA can then be used to identify whether or not the COVID-19 genetic sequence is present. If present, a positive result is indicated; if not the machine will indicate a negative result. However, PCR tests can sometimes present a false positive or a false negative result. A false positive is highly unlikely, however, false negatives are far more common as the machines may not detect the presence of viral genetic material in the early stages of infection.
Citations:
“Understanding COVID-19 PCR Testing.” Genome.gov, 2022, www.genome.gov/about-genomics/fact-sheets/Understanding-COVID-19-PCR-Testing.
“COVID-19 Diagnostic Testing - Mayo Clinic.” Mayoclinic.org, 2022, www.mayoclinic.org/tests-procedures/covid-19-diagnostic-test/about/pac-20488900.
“PCR Tests.” Medlineplus.gov, 2021, medlineplus.gov/lab-tests/pcr-tests/.
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