von Willebrand Disease Reflexive Profile

Use

vWF is produced by megakaryocytes and endothelial cells.2 The vWF protein polymerizes in plasma into multimers of up to 100 subunits that range in size from 0.5 to 20 million daltons.1,2 vWF's plasma half-life is about 24 hours. vWF performs two major functions in hemostasis.1,2 vWF acts a cross-linking protein that connects platelets to each other and to subendothelial cells at the site of vascular damage. This functionality is dependent on the presence of high molecular weight multimers of vWF. vWF also serves as an obligate carrier of factor VIII in plasma. Functional vWF serves to protect factor VIII from proteolytic degradation and effectively increases its half-life fivefold.4 Effective factor VIII binding is not dependent on the presence of large multimeric vWF complexes.3 The assessment of vWF activity requires two tests to evaluate these two functions. The vWF activity (ristocetin cofactor) assay reflects the effectiveness of the patient vWF in supporting platelet adhesion. Factor VIII levels can be diminished due to low vWF levels or due to ineffective factor VIII binding by a defective vWF.