Assessment of Hemostasis

Contact of platelets with subendothelial collagen induces platelet adhesion, a reaction mediated by von Willebrand factor. Adhesion is followed by platelet conformation change and release of substances such as serotonin, platelet factor-4 (PF-4), s-thromboglobulin, and factor Va. ADP release induces platelet activation, exposure of fibrinogen receptors and thus aggregation. The final product of the primary platelet activation is the platelet (“white”) clot, which is stabilized and stregthened by the fibrin clot.