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The page below is a sample from the LabCE course Antiplatelet and Anticoagulant Pharmacology for the Laboratory Professional. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Clinical Correlation: von Willebrand Disease (vWD)

Von Willebrand Disease (vWD) is the most common inherited hemostasis disorder. Decreased amounts of von Willebrand factor (vWF) results in decreased platelet adherence to the damaged blood vessel wall. This causes increased bleeding. Bleeding in platelet disorders is different from bleeding in coagulation factor deficiencies. Bleeding in platelet disorders such as von Willebrand disease presents as bleeding from the skin, oral, and nasal mucosa, the GI tract, blood in the urine, and blood from the vagina.
Laboratory diagnosis of vWD:
  • Normal platelet count and normal peripheral blood smear.
  • Increased bleeding time and abnormal platelet function analysis assays.
  • Decreased vWF (may be referred to as factor VIII antigen assay).
  • PTT may be elevated due to the relationship of vWF and factor III. Recall that factor VIII is tested in the aPTT assay. PT will be normal.
  • Abnormal ristocetin-induced platelet aggregation assay. Ristocetin is an artificial endothelial surface. In vWD, platelets can't adhere to any endothelial surface, thus patient's with vWD produce an abnormal result with this assay.
Treatment of vWD:
  • Desmopressin, if symptoms are mild. Desmopressin causes the release of vWF.
  • If severe, factor VIII replacement.