The presence of inhibitory compounds in the extracted RNA and the extent of inhibition can be determined by semiquantitative rRT-PCR of an RNA template that is present in the sample, added to it prior to extraction, or introduced into the rRT-PCR mix. Natural or modified, encapsulated coliphage MS2 RNA is one source of protected RNA that has been used as a noncompetitive external RNA template control [5, 12, 13, 14] .