What Is PCR?

Real-time polymerase chain reaction (PCR, real-time PCR, or qPCR) is a molecular diagnostic testing technique of identifying whether a target genetic sequence of DNA or RNA (e.g. of a cancer gene, a bacteria or virus in humans, animals, or in the food distribution supply chain, or specific attributes of a seed variety in agriculture) is present in a given sample.

The technique is used to amplify—or make exponentially more copies of—the genetic material through a series of heating and cooling cycles, which is then identified by laboratory equipment. If amplification is detected, that means the bacteria, virus, or cancer gene in question was present in the sample — a positive result. If not, that means the target sequence was not present — a negative result.

Real-time PCR is a variety of PCR that allows for monitoring of the amplification process in real-time, and can even be used to quantify, or count, the amount of DNA/RNA present.

Real-time PCR is one of the premier methods of detecting a bacteria or virus on the molecular level, with higher degrees of accuracy than microscopy (peering through a microscope to see if certain bacteria are present) and considerably faster than the days or weeks it takes to grow a culture to determine if someone has a disease. Such inaccuracies and delays can mean the difference between life and death. It is also the only way to identify the presence of a gene that indicates a predisposition towards cancer or other diseases.

PCR has nearly endless applications, from detecting the presence or absence of various pathogens in body fluids, identifying both spontaneous and inherited malignant changes in DNA, determining whether the intended modifications of crops took place, allowing for a variety of testing seeds, and much, much more.