Real time PCR is a laboratory method to make multiple copies of a specific genetic sequence for data analysis. It uses an enzyme reverse transcriptase to change a precise piece of RNA into a similar piece of DNA. Another enzyme, DNA polymerase, then amplifies this piece of DNA. The amplified DNA copies help determine if a gene makes a particular mRNA molecule. RT-PCR is also best to find specific changes in a chromosome or gene or activate genes. It may help diagnose a disease like cancer. It helps learn the RNA of certain viruses, such as the human immunodeficiency virus and the hepatitis C virus and helps diagnose and monitor infection.