Our December 2024 Quick Question, “How do you test for VWD subtype 2B?” attracted 31 responses as follows:
- RIPA: 15 [48%]
- VWFAg: 2 [7%]
- VWF:CB: 5 [16%]
- VWF:RCo: 6 [19%]
- Multimeric analysis: 3 [10%]
Our question drew this comprehensive discussion from Dr. Emmanuel Favaloro on Tuesday, December 12, 2023: Hi George, I have been following the results for this question for a few weeks now, and thought I should comment. Feel free to hold off posting this comment until the question has run its course.
Of course, the answer is more complex than any individual test, but the majority response [RIPA] is the most correct. For 2B VWD, you should see enhanced responsiveness to low-dose ristocetin in the RIPA assay. The other assays listed [VWF:Ag, VWF:CB, VWF:RCo, multimers] are certainly important for identifying type 2B VWD as a VWD, but won’t enable discrimination of 2B VWD from other VWD types. But, as I said, it’s more complicated. Enhanced responsiveness to low-dose ristocetin in the RIPA assay is characteristic of type 2B VWD, but may alternatively point to its ‘cousin’ platelet type [PT] VWD. 2B VWD reflects a hyper-functional form of VWF that ‘spontaneously’ binds to its platelet receptor [GPIb]. In contrast, PT VWD reflects a hyper-functional form of GPIb that ‘spontaneously’ binds to plasma VWF. 2B VWD is about 10 times more common than PT VWD but reflects <5% of all VWD. You can distinguish 2B VWD from PT VWD using RIPA mixing studies [1] or by assessing for genetic variants in VWF and GPIb. Interestingly, the latest VWD diagnosis guidelines [2] favor genetic testing ahead of RIPA.
1. Frontroth JP, Favaloro EJ. Ristocetin-induced platelet aggregation [RIPA] and RIPA mixing studies. Methods Mol Biol. 2017;1646:473–94. doi:10.1007/978-1-4939-7196-1_35. PMID: 28804849
2. James PD, Connell NT, Ameer B, et al. ASH ISTH NHF WFH 2021 guidelines on the diagnosis of von Willebrand disease. Blood Adv. 2021;;5:280–300. doi: 10.1182/bloodadvances.2020003265. PMID: 33570651; PMCID: PMC7805340.
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