Due to the limitations of reverse-transcriptase-PCR (RT-PCR) and the fact that the method is only semi-quantitative, the combination of real-time PCR and RT-PCR has become the preferred method for quantifying gene expression or verifying results from array analysis.
Real-time RT-PCR is the most sensitive method for evaluating RNA. Less sensitive methods for quantifying RNA include northern blotting, in situ hybridization, and ribonuclease protection assays (RPAs).
Though northern blotting and RPAs are the gold standards for mRNA analysis, they require larger amounts of initial material. Therefore, real-time RT-PCR is the preferred method when available amounts of RNA are low.