Polymerase chain reaction, PCR, is an efficient and cost-effective way to copy or "amplify" small segments of DNA or RNA. Using PCR, millions of copies of a section of DNA are made in just a few hours, yielding enough DNA required for analysis. This innovative yet simple method allows clinicians to diagnose and monitor diseases using a minimal amount of sample, such as blood or tissue. It is a natural process of DNA replication which occurs in vitro, or outside of the body in a laboratory. It is the simplest form of reaction occurs, when a DNA sample and a DNA polymerase, nucleotides, primers and other reagents are added to a sample tube. PCR enables the monitoring of the amount of a virus present or viral load, in a person’s body, apart from detecting diseases in a sample.