4. Discussion
Circulating miRNA may have great potential as biomarkers for
many diseases, and many studies have addressed associations
between disease status and miRNA levels in biobanked plasma or
serum samples [22–24]. As platelets contain large amounts of
miRNA [25], residual platelets may contribute significantly to the
miRNA levels in plasma, and therefore platelets should be removed prior to miRNA analysis. During freezing and/or thawing of
the plasma, miRNAs may be released from residual platelets and
contribute to the miRNA levels even despite of an additional
centrifugation step after thawing of the plasma. To evaluate biobanked plasma as a suitable material for miRNA-analysis, or
whether it can be transformed into such, we performed a range of
centrifugation steps on biobanked plasma samples, after which we
analyzed the plasma preparations for their residual platelet contents as well as miRNA levels.
When using our standard procedure for biobanking (centrifugation of whole blood for 10 min at 2000 g) plasma contained
a relatively high number of platelets (Fig. 2). A further centrifugation of the biobanked plasma for 15 min at 3000 g reduced,
but did not fully eliminate residual platelets, whereas a two-step
centrifugation at these conditions or a 30 min centrifugation at