PCR can be modified for the amplification of RNA with one additional step prior to the PCR process -- the addition of a retrovirus enzyme called reverse transcriptase. Reverse transcriptase is used to create a copy of DNA using the original RNA specimen. Though there are thermostable polymerases that have reverse transcriptase capabilities, they are not commonly used.
Reverse transcriptase PCR (RT-PCR) is used for the detection of viruses, such as HIV, that have an RNA genome. RT-PCR methods provide early detection of infection, even before the formation of antibodies. Therefore, it is a particularly useful method for HIV and hepatitis C virus (HCV) detection in blood bank nucleic acid testing.
In addition to testing for HIV and HCV, RT-PCR is also used for detection of influenza A virus and other microorganisms where the target is RNA.
RT-PCR is commonly combined with real time PCR.