3321 - What is the purpose of the C. elegans miR-39 spike-in control in the miRNeasy Serum/Plasma kit?

Since there is no clear consensus in the research community about which endogenous RNA should be used as a reference gene for miRNA expression profiling in serum or plasma, many researchers choose to add a synthetic  miRNA as a spike-in control.  This spike-in control can then be used for sample-to-sample normalization of RNA recovery and reverse transcriptase efficiency (combined).