Recommendation to adopt the type 1C VWD nomenclature into the classification of von Willebrand disease: communication from the ISTH Scientific and Standardisation Subcommittee on von Willebrand Factor.

BACKGROUND: Von Willebrand disease (VWD) has 6 categories of either quantitative or qualitative abnormality of von Willebrand factor (VWF). As our understanding of the pathophysiology of VWD improves, there is a need to re-evaluate the classification system consistently. The International Society of Thrombosis and Haemostasis (ISTH) VWF Scientific and standardisation committee (SSC) sought endorsement from the ISTH membership to change the VWD classification to include type 1C VWD (increased VWF clearance) and Type 2M-P VWD (platelet binding defect) and Type 2M-C VWD (collagen binding defect).

METHOD: After approval of the VWF SSC, the proposals and scientific justification for each VWD classification change were presented at the ISTH VWF SSC virtual 2020 Congress. This was followed by an online vote of the ISTH community promoted via the ISTH Congress, the VWF SSC mailing list, and social media. It was open from July 2020 to December 2020, with an a priori criteria of at least 75% approval to endorse the proposed subtypes.

RESULTS: The inclusion of Type 1C VWD was confirmed with an approval of 94.2%. Although type 2M-P VWD and Type 2M-C VWD had merit, they did not meet the required threshold for approval (71.9%).

CONCLUSION: There was an overwhelming endorsement for including Type 1C in the VWD classification, which occurs in around 20% of Type 1 VWD patients with a shortened VWF survival. Although generally supported, the threshold was not met to include the subcategorization of Type 2M-P VWD and Type 2M-C VWD.