April 2026 QQ Results: VWF Activity

Our April 2026 Quick Question reprises our 2023 QQ that asked, How do you measure VWF activity. Our 29 respondents answered as follows:

1. VWF:RCo: 16 (56%)
2. VWF:GP1bR: 6 (21%)
3. VWF:GP1bM: 5 (16%)
4. VWF:CB: 2 (7%)
5. RIPA: 0

Our 4-1-2026 introductory QQ post attracted this comment from Dr. Emmanual Favaloro, Sydney, NSW, Australia: Hi George, of course, the question only allows one answer; in 2026, we use VWF:GPIbM, VWF:CB, and if needed RIPA. They all measure different aspects of VWF function. I predict VWF:RCo and VWF:GPIbM will be popular with the North American crowd, as they are FDA cleared. I also suspect that some respondents will pick VWF:RCo even if they perform a VWF:GPIbR (since this is how the manufacturer markets the product–perhaps using VWF:RCo as a predicate device for FDA clearance?).

If you click back to our 2023 QQ, you will see the same proportions, indicating that we continue to use the imprecise VWF:RCo. Apparently, we’ve made no progress, perhaps because we know that the VWF:GP1bR relies on ristocetin, and the VWF:GP1bM avoids the ristocetin requirement as it employs a VWF-sensitive platelet GP1b receptor reagent, similar to the so-called “Platelet-type VWD” in which the platelet GP1b receptor activity is enhanced by a gain-of-function mutation, thus increasing VWF binding.

We thank Dr. Favaloro for his comment. As we know,  “VWF Activity” is better expressed as VWF-platelet binding capacity. The RIPA assay uses a reduced ristocetin level and the patient’s own platelets. Agglutination implies VWF subtype 2B with increased platelet binding. The VWF:CB measures VWF‘s ability to bind collagen.

Sarkar MK, Fritsma GA. Hemorrhagic Disorders and Laboratory Assessment. In Keohane EM, Butina MM, Mirza KM, Walenga JM. Rodak’s Hematology; Clinical Principles and Applications, 7th edition, Elsevier, 2025.