RT-PCR is short for Reverse Transcription-Polymerase Chain Reaction. RT-PCR is a technique in which an RNA strand is "reverse" transcribed into its DNA complement, followed by amplification of the resulting DNA using a polymerase chain reaction (PCR).
Transcribing an RNA strand into its DNA complement is termed reverse transcription (RT), and is accomplished through the use of an RNA-dependent DNA polymerase (reverse transcriptase). Afterwards, a second strand of DNA is synthesized through the use of a deoxyoligonucleotide primer and a DNA-dependent DNA polymerase. The complementary DNA and its anti-sense counterpart are then exponentially amplified via a polymerase chain reaction (PCR).
The exponential amplification via RT-PCR provides for a highly sensitive technique, where very low copy number RNAs can be detected. RT-PCR is widely used in the diagnosis of genetic diseases and, quantitatively, in the determination of the abundance of specific RNA species (as a measure of gene expression). (See also Northern blot.)
RT-PCR also sometimes refers to Real-Time PCR, which is an extension of the original PCR procedure and designed for quantitative purposes. Real-Time refers to the fact that quantitative PCR machines monitor and display the progress of the PCR reactions as they proceed. To avoid confusion between the two techniques described as "RT", the term quantitative PCR or quantitative RT-PCR is preferred when referring to the real-time, quantitative analysis.