All RNA samples that are brought for library preparation need to pass a sample QC, which includes Qubit quantification and Bioanalyzer run. In this case, the Bioanalyzer informs us about the quality of the RNA, and gives a RNA Integrity (RIN) number. Good quality RNA typically has a RIN number above 7 or so. Low RIN numbers indicate RNA degradation. We can still prepare libraries with degraded RNA, but certain parameters need to be adjusted.