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Von Willebrand Disease (VWD)
Part 3: VWF Activity Assay

A New von Willebrand Factor Activity Assay and Testing Algorithm

Problems with VWF:RCo Assay

Slide 4

June 2011

Despite its vibrant history and the status of being considered as the reference method, VWF ristocetin cofactor activity assay is problematic. It is imprecise with an average coefficient variation of 20% to 30%, possibly due to diversity of the reagent donor platelets and complexity of platelet aggregation kinetics. It has suboptimal lower and higher detection limit. Currently, the lower detection limit of VWF ristocetin cofactor activity is 12.5 IU/dL. In addition, VWF ristocetin cofactor activity is very imprecise when VWF antigen is lower than 30 IU/dL or higher than 200 IU/dL. And finally, VWF ristocetin cofactor activity over antigen ratio at a cut off of 0.7 is generally insensitive for acquired VWF abnormality when there are subtle losses of the highest molecular weight multimers.

Problems with VWF:RCo Assay


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