VWF and von Willebrand disease (hereditary or acquired): For instance, patients with a bleeding tendency, VWF:Ag 30 to 50%, with normal VWF activity/Ag ratios, are classified as VWD type 1 patients by the current ASH ISTH NHF WFH (American Society of Hematology, International Society on Thrombosis and Haemostasis, National Hemophilia Foundation, World Federation of Hemophilia) 2021 guidelines.184Historically, these patients were considered to have “low VWF” and were not diagnosed with VWD.