The fold change in one tested HKG (target gene) was normalized to the 18S rRNA (reference gene) and compared to the highest quality sample (calibrator sample), using the following formula: Fold change = 2 ÀDDCt , where DDCt = (C t-target À C t-reference ) sample-n À (C t-target À C t-reference ) calibrator-sample . Sample-n corresponds to any sample for the target gene normalized to the reference gene and calibrator-sample represents the expression level (1·) of the target gene normalized to the reference gene considering the highest quality sample. Mean 2 ÀDDCt and SD were calculated, considering the samples either individually or grouped by quality metrics categories, based on RIN metrics or DegFact values, together with the lower and upper bound mean of 95% Intervals of Confidence (IC). Using this analysis, if the expression levels of the HKG are not affected by the RNA degradation, the values of the mean fold change at each condition should be very close to 1 (since 2 0 = 1) (27) .