Pre-storage centrifugation conditions have significant impact on measured microRNA levels in biobanked EDTA plasma samples

•Platelet count vary significantly in standard biobanked EDTA plasma.•Residual platelets can be removed by centrifugation of thawed biobanked samples.•Re-centrifugation of biobanked plasma cannot eliminate contaminating platelet miRNAs.•Pre-storage centrifugation conditions have large impact on measured miRNA levels.

BackgroundIn the past few years, an increasing number of studies have reported the potential use of microRNAs (miRNA) as circulating biomarkers for diagnosis or prognosis of a wide variety of diseases. There is, however, a lack of reproducibility between studies. Due to the high miRNA content in platelets this may partly be explained by residual platelets in the plasma samples used. When collecting fresh plasma samples, it is possible to produce cell-free/platelet-poor plasma by centrifugation. In this study, we systematically investigated whether biobanked EDTA plasma samples could be processed to be suitable for miRNA analysis.Materials and methodsBlood samples were collected from ten healthy volunteers and centrifuged to produce platelet-poor-plasma (PPP) and standard biobank plasma. After one week at −80 °C the biobanked EDTA plasma was re-centrifuged by different steps to remove residual platelets. Using RT-qPCR the levels of 14 miRNAs in the different plasma preparations were compared to that of PPP.ResultsWe were able to remove residual platelets from biobanked EDTA plasma by re-centrifugation of the thawed samples. Nevertheless, for most of the investigated miRNAs, the miRNA level was significantly higher in the re-centrifuged biobanked plasma compared to PPP, even when the platelet count was reduced to 0–1×109/L.ConclusionWe found, that pre-storage centrifugation conditions have a significant impact on the measured EDTA plasma level of miRNAs known to be present in platelets. Even for the miRNAs found to be less effected, we showed that a 1.5–3 fold change in plasma levels may possible be caused by or easily overseen due to sample preparation and/or storage.