Platelet Disorders and Von Willebrand Disease

Platelets are highly complex cells that participate in critical steps central to hemostasis and thrombosis, including adhesion to subendothelium, aggregation, secretion of granule contents, and provision of membrane surface for activation of coagulation factors. Abnormalities of either platelet number or platelet function can play an important role in the balance of hemostasis and thrombosis. Almost unique to laboratory medicine and pathology, assessment of platelet pathology may be performed in real time upon living cells obtained from the patient. A number of inherited and acquired disorders, autoimmune processes, and drugs affect platelet counts and platelet function. In a large proportion of patients with inherited platelet disorders, the underlying genetic and molecular mechanisms are unknown. Von Willebrand factor (vWF) is a multimeric protein synthesized by endothelial cells and megakaryocytes that plays a central role in platelet adhesive interactions. Abnormalities related to vWF lead to the bleeding disorder von Willebrand disease and thrombotic thrombocytopenic purpura, associated with vascular occlusions and hemolysis.