The characterization and impact of microparticles on haemostasis within fresh‐frozen plasma

Background We have previously demonstrated that clot formation in fresh‐frozen plasma (FFP) is influenced by the presence of microparticles (MP). In this study, the cellular source(s), properties and influence of MPs on clot formation within FFP were further characterized. Methods Fresh‐frozen plasma was prepared after an overnight hold of whole blood at 4°C. We examined the effect of a 0·2 µm filtration device designed to remove cellular MPs on thrombin generation test (TGT) and Thrombelastography (TEG®) as well as clotting factors and physiological inhibitors: prothrombin time (PT); activated partial thromboplastin time (APTT), fibrinogen (Fg), factor VIII (FVIII), von Willebrand factor antigen (VWF:Ag), antithrombin III (AT‐III) and protein C (PC). MPs were measured using a functional assay and also by flow cytometry. Results Microparticle levels by functional assay were reduced by filtration (pre‐ 5·11 vs. post‐ 4·43 nmol/l phosphatidylserine equivalent, P < 0·0001). Flow cytometry showed that the most numerous MPs were derived from red blood cells, with ~87% binding annexin V, most of which (94%) were removed by filtration. MP removal had minimal effect on the PT, APTT, Fg, VWF:Ag, AT‐III or PC or FVIII, but a major effect on TGT (endogenous thrombin potential: pre‐ 1722 vs. post‐ 990 nM thrombin, P < 0·0001; peak thrombin: pre‐ 91 vs. post‐ 44 nM thrombin, P < 0·0001), which in turn reflected the changes seen in TEG®, where post‐filtration clots started forming more slowly and the rate of clot formation was reduced. Conclusion These data suggest that MPs contribute towards clot formation in FFP.