What is von Willebrand factor antigen (vWF:Ag)?

Updated: Jul 19, 2021
  • Author: Vadim Kostousov, MD; Chief Editor: Eric B Staros, MD  more...
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vWF is a multimeric protein (molecular weight varies from 500-20,000 kDa) that is assembled from identical monomers in endothelial cells and megakaryocytes and can be released from endothelium and platelets upon activation. The half-life of vWF is approximately 12 hours (range, 9-15 h), and its clearance is faster in persons with blood type 0. [4] The main function of vWF is to support platelet adhesion to injured subendothelium in order to form a hemostatic plug. In addition, vWF is a carrier protein for factor VIII and prevents its proteolytic degradation in plasma.

The vWF:Ag assay evaluates the total protein amount in plasma. The most common in clinical laboratories are latex immunoturbidimetric assays, in which the agglutination of latex microparticles coated with anti-vWF antibodies is proportional to vWF:Ag. Cloudy plasma may result in underestimation of vWF:Ag levels, while the presence of rheumatoid factor in the plasma can produce overestimation.

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