Coagulation laboratory tests
von Willebrand factor activity

Topic Completed: 1 November 2012

Minor changes: 28 September 2020

Copyright: 2002-2020,, Inc.

PubMed Search: von Willebrand factor activity [title]

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Definition / general | Laboratory
Cite this page: Parsons JC. von Willebrand factor activity. website. Accessed December 5th, 2020.
Definition / general
  • Also called ristocetin cofactor activity
  • Ristocetin is an antibiotic that causes vWF to bind to and activate platelets
  • Test measures function of von Willebrand factor
  • Platelets from healthy individuals are mixed with standard concentrations of ristocetin, and patient plasma is added to cause platelet agglutination (measured in aggregometer), which is proportional to the vWF concentration
  • Used to confirm type 2B von Willebrands disease (increased agglutination due to increased affinity of vWF for GPIb); similar results for platelet type von Willebrands disease (although the defect is in GPIb)

  • Note: aggregation of platelets implies linkage via fibrinogen and GP IIb / IIIa; ristocetin links platelets through vWF and GP Ib; appropriate term is actually agglutination

  • Other functional tests: collagen-binding ELISA assay, functional vWF binds to collagen and is detected (Br J Haematol 2002;116:187)
  • Low dose ristocetin platelet aggregation assay
    • To diagnose type 2B von Willebrand disease
    • Similar to von Willebrand factor activity test, but uses patients platelets and lower dose of ristocetin
    • Platelets from patient are mixed with standard concentrations of ristocetin and patient plasma is added to cause platelet agglutination (measured in aggregometer)
    • Increased aggregation in type 2B vWD in this assay due to GP Ib mutation, which increases affinity for vWF
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