What is von Willebrand factor ristocetin cofactor (vWF:RCo)?

Updated: Feb 12, 2020
  • Author: Vadim Kostousov, MD; Chief Editor: Eric B Staros, MD  more...
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von Willebrand factor (vWF) is multimeric glycoprotein (molecular weight varies from 1000-20,000 kDa) that is assembled from identical monomers in endothelial cells and megakaryocytes possibly released from endothelium and platelets upon their 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. [5]

The main function of vWF is to support platelet adhesion to injured subendothelium in order to form hemostatic plug. Also vWF is a carrier protein for factor VIII and prevents its proteolysis degradation in plasma. vWF:RCo assay evaluates protein functional activity; platelet aggregation to vWF in the presence of ristocetin is proportional to hemostatically active fraction of vWF. [5, 3]

In order to overcome poor sensitivity of the standard assay at lower activity of vWF:RCo (less than 20-30%), a modified protocol of vWF:RCo assay was implemented and validated. [6, 7] Also, assays of vWF activity measurement were developed that utilize microparticles covered with recombinant platelet receptors to glycoprotein Ib, which bind to vWF (vWF:GPIb) in the presence or absence of ristocetin; [8] these could replace the standard vWF:RCo activity assay in the future.

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