Model for the relationship of VWF level to risk of bleeding, thrombosis, and VWF mutations. The thick solid line indicates the frequency distribution of VWF levels (IU/dL) for the population, and 95% of values lie between 50 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. Although previous versions of this figure separated type 1 VWD as <20 to 30 IU/dL and low VWF as 30 to 50 IU/dL, data from the current study by Atiq et al suggest that individuals with levels 30% to 50% are a result of physiological aging. Modified from the review by Sadler.⁶