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Coagulation

Coagulation laboratory tests

von Willebrand factor activity


Reviewer: Jeremy Parsons, M.D. (see Reviewers page)
Revised: 11 February 2013, last major update November 2012
Copyright: (c) 2002-2013, PathologyOutlines.com, Inc.

General
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● 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 Willebrand’s disease (increased agglutination due to increased affinity of vWF for GPIb); similar results for platelet type von Willebrand’s 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
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● To diagnose type 2B von Willebrand disease
● Similar to von Willebrand factor activity test, but uses patient’s 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

End of Coagulation > Coagulation laboratory tests > von Willebrand factor activity


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