RT-PCR (reverse transcription-polymerase chain reaction) is a laboratory method used to make many copies of a specific genetic sequence for analysis. It uses an enzyme called reverse transcriptase to change a specific piece of RNA into a matching piece of DNA. This piece of DNA is then amplified (made in large numbers) by another enzyme called DNA polymerase. The amplified DNA copies help tell whether a specific mRNA molecule is being made by a gene. RT-PCR may be used to look for certain changes in a gene or chromosome or for activation of certain genes, which may help diagnose a disease, such as cancer. It may also be used to study the RNA of certain viruses, such as the human immunodeficiency virus (HIV) and the hepatitis C virus, to help diagnose and monitor infection. 

Having been around since 1983, RT-PCR  is the most sensitive technique for quantitative and mRNA detection currently available and is considered the “gold standard” for test results.