Model for the relationship of von Willebrand factor (VWF) level to risk of bleeding, thrombosis, andVWFmutations. The thick solid line indicates the frequency distribution of VWF levels (IU/dL) for the population, and 95% of values lie between 50 IU/dL and 200 IU/dL. Also shown are estimates of the relative risk of bleeding (short-dashed line, magenta shading), thrombosis (long-dashed line, green shading), and mutation within the VWF gene (thin solid line, orange shading) as a function of VWF level; the relative risk is defined as 1.0 at the population mean VWF level of 100 IU/dL. As indicated at the top, VWF levels < 20 IU/dL are generally consistent with a diagnosis of VWD type 1, low VWF levels (30 to 50 IU/dL) confer a modest risk of bleeding, and high VWF levels (> 200 IU/dL) confer a modest risk of thrombosis.