PCR Test Basics: How They Work

PCR tests and similar tests are the “gold standard” for detecting the virus that causes COVID-19. PCR stands for “polymerase chain reaction,” which is a commonly used biochemical reaction that makes copies of short segments of genetic material. Here’s how it works after your provider swabs your nose:

The sample is taken to a lab where the genetic material is extracted. This genetic material then serves as the template for the PCR reaction. In the case of COVID-19 PCR tests, the template is the RNA genome of the virus. A protein called a polymerase and short segments of DNA called primers are added. Polymerase proteins are a class of proteins that can make DNA copies from RNA or DNA templates. Primers tell the polymerase what part of the template to copy.

The test is run on a machine. If copies of the template are made this is called amplification and can be detected by the machine. If amplification is detected, the test is positive.  If amplification does not happen, the test is negative.

A side note, your test results may have the abbreviation NAAT or NAA instead of PCR.  This stands for “nucleic acid amplification test” and is a term that includes PCR tests as well as similar, functionally equivalent test types that use a different reaction.

For more details of how PCR reactions work, read here.

Last update: December 17, 2021 at 9:30 am ET

Science review: SGB, JAB