February, 2023 Quick Question: VWF Activity Assays

Our February 2023 Quick Question, “What VWF activity assay do you use?” attracted 32 responses. Here are the results:

1. Automated VWF:RCo: 12 [38%]
2. VWF:RCo: 10 [31%]
3. VWF:GP1bR: 3 [9%]
4. VWF:GP 1bM: 4 [13%]
5. VWF:Ab: 2 [6%]
6. VWF:CB: 1 [3%]

Although the aggregometer-based ristocetin cofactor activity assay [VWF:RCo] is criticized for poor reproducibility, with interassay CV >7%, the automated VWF:RCo performed using Sysmex equipment offers an acceptable interassay CV of 3.8%.

The VWF:GP1bR [the R stands for ristocetin or recombinant] employs recombinant glycoprotein 1b tethered to microparticles that bind the A1 domain of high MW VWF in the presence of ristocetin, eliminating the use of preserved whole platelets as are used in the VWF:RCo assay.

The VWF:GP1bM [M stands for modified or mutated] assay employs a gain-of-function high-affinity recombinant GPIb target protein that resembles the GPIb of PT–VWD [Pseudo-VWD] platelets. GPIb-coated microparticles bind the A1 domain of HMW-VWF without the need for ristocetin. The VWF:GP1bM is FDA-approved and is gradually replacing VWF:RCo for its acceptable CVs and functionality.

The VWF:Ab employs a polyclonal antibody to high MW VWF that claims to measure VWF activity.

The VWF:CB measures collagen binding, a VWF property separate from its platelet membrane GP1b binding function.

Thank you to our participants for your responses, and please send us your comments.