Reduced von Willebrand factor activity

What it means

Decreased activity of von Willebrand factor. Von Willebrand factor mediates the adhesion of platelets to the collagen exposed on endothelial cell surfaces.

Von Willebrand factor (VWF) is a key hemostatic protein, but documenting its function through laboratory tests is not always straightforward. VWF serves as a carrier protein for factor VIII (FVIII), and also facilitates platelet adhesion through its interaction with platelet GPIb on the platelet surface and through its binding to the subendothelial matrix. This interaction is driven in vivo by shear stress, which induces a conformational change in VWF that allows it to bind platelet GPIb. In vitro, however, this interaction is induced by the antibiotic ristocetin, which enables VWF and platelet GPIb to interact in the absence of shear forces. Laboratory testing of VWF utilizes ristocetin in the VWF ristocetin cofactor activity assay (VWF:RCo), which is a measure of VWF binding to platelets, or by ristocetin-induced platelet aggregation (RIPA).

Rare diseases that can present with this4

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Decreased von willebrand factor activity