VWF Activity Assay

Preliminary to our February 2023 Quick Question, here is a detailed January 2023 CAP Today article entitled “Ins and Outs of von Willebrand Factor Activity Assays.” In addition to the time-honored, but imprecise optical aggregometry-based von Willebrand Ristocetin Cofactor  [VWF:RCo] assay, we now have these activity assays that, except for VWF:RCo, function without reagent-platelets…

• VWF:RCo: automated
• VWF:GP1bR: automated; recombinant GP1b immunologically bound to latex or magnetic particles. Add ristocetin and patient plasma, measure agglutination
• VWF:GP1bM: automated; recombinant gain of function GP1b immunologically bound to latex or magnetic particles. Add patient plasma, measure agglutination–FDA cleared, requires no ristocetin
• VWF:Ab: automated; latex beads coated with monoclonal anti-VWF A1 domain, add patient plasma, measure agglutination–FDA cleared, no ristocetin
• VWF:CB: automated, type III collagen coated on magnetic beads, add patient plasma, chemiluminescent assay.

The VWF:RCo uses reagent platelets and the VWF:CB uses collagen. The other three assays measure VWF platelet-binding activity without reagent platelets. Refer to the linked CAP Today article, then go on to answer our February Quick Question.