3. MiRNA levels
To evaluate the effect on miRNA levels of different residual
platelet count in biobanked plasma samples, we compared the
miRNA levels in the different plasma preparations with the levels
in PPP (Table 1 and Supplementary Figs. 1 and 2). When preparing
the biobank A2/B2 samples, an additional centrifugation step was
used as an effort to eliminate any remaining platelets from the
biobank A/B samples. Despite this additional centrifugation step,
four biobank A2 samples still contained a small amount of platelets, and to ensure a sample population with minimal platelet
contamination, we chose not to use these four samples for miRNAanalysis. Therefore, miRNA-analysis was performed on PPP, biobank A, biobank B and biobank B2 samples from ten volunteers,
and on the six biobank A2 samples with a platelet count of
0–1 109/L.
MiRNA levels were normalized using either the exogenous celmiR-39 or the endogenous miR-16 as reference gene. When normalized to cel-miR-39, levels of miR-16 were found to be significantly (po0.05) higher in biobank A, A2 and B samples compared to PPP samples (1.6–2.6 fold in average). Therefore, the fold
changes in miRNA levels between the different plasma preparations and PPP found for the other investigated miRNAs were lower