ABO blood group and VWF:Ag level. (A) Graph showing the relative proportion of ABO blood groups in index cases with VWF:Ag level more than 0.30 IU/mL compared with the Canadian population. The difference between the 2 groups in the frequency of blood group O (marked with *) is highly statistically significant (P = .002, Pearson chi-square). (B) Graph showing the relative proportion of ABO blood groups in index cases with VWF:Ag level of 0.30 IU/mL or less compared with the Canadian population. The difference in the frequency of blood group O between patients and the Canadian population is not statistically significant. % on the y axis refers to percentage of population.