Low VWF - unravelling an enigma wrapped in a conundrum.

The 2021 ASH ISTH NHF WFH guidelines recommendation that patients with VWF levels of 30-50 IU/dL and an increased bleeding phenotype be categorized as type 1 VWD rather than Low VWF has proved controversial. However, in support of that decision, recent data have demonstrated that individuals with partial quantitative VWF deficiency exhibit an age-dependent evolving phenotype and confirmed that Low VWF represents a sub-group within heterogeneous type 1 VWD. Nonetheless, type 1 VWD heterogeneity continues to pose significant diagnostic challenges. In this Forum Article, we address outstanding issues critical to preventing the inappropriate overdiagnosis of type 1 VWD, while maximizing access to healthcare and minimizing diagnostic delays. In addition, we propose an algorithm for type 1 VWD diagnosis. This algorithm pays special attention to individuals with plasma VWF levels in the 30-50 IU/dL range who have no or minimal bleeding history and have not yet been exposed to significant hemostatic challenges.