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Monitoring von Willebrand Disease Therapy

Eight participants answered our June 16-21 hemostasis question asking how we monitor von Willebrand disease therapy. Three employ the von Willebrand ristocetin cofactor assay (VWF:RCo, VWF activity). This is the method recommended by the Scientific Sub-Committee on von Willebrand Factor of the International Society of Thrombosis and Haemostasis (ISTH-SSC on VWF). However, four prefer the von Willebrand factor antigen (VWF:Ag) assay. One respondent uses the factor VIII activity (FVIII:C) assay, and none use the collagen binding assay (VWF:CB). 
It is curious that although ISTH recommends VWF:RCo as the reference assay, a majority (well, plurality) prefer the VWF:Ag. The reasons for this are compelling…

• CV% for VWF:Ag ranges 10-15% compared to VWF:RCo, 20 to 40% (recent CAP surveys)
• There are speedy VWF:Ag methods available; for instance, Diagnostica Stago distributes the LIAtest, which provides a 10-minute turn-around.
• The VWF:RCo assay requires tedious and demanding manual aggregometry except in those labs that have the Siemens (Dade-Behring) BCS equipped with the automated ristocetin assay. Dade calls this the BC von Willebrand Reagent®. Company claims to the contrary, this doesn’t work on non-Dade instruments.
• Although we employ the VWF:RCo and VWF:Ag in tandem to assign VWD type, the therapeutic VWF:Ag is proportional to VWF:RCo, so the VWF:Ag is a reliable substitute.
• Ristocetin reagent has a single source and is not always available, for instance, as of today, June 23, 2008, it is unavailable.

Thank you for your responses and watch for this week’s question. Geo

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