In order to firmly establish a normal range for von Willebrand factor antigen (vWF:Ag), we determined plasma vWF:Ag concentrations in 1,117 volunteer blood donors by quantitative immunoelectrophoresis. The presence of the ABO blood group has a significant influence on vWF:Ag values; individuals with blood group O had the lowest mean vWF:Ag level (74.8 U/dL), followed by group A (105.9 U/dL), then group B (116.9 U/dL), and finally group AB (123.3 U/dL). Multiple regression analysis revealed that age significantly correlated with vWF:Ag levels in each blood group. We then performed reverse ABO typing on stored plasma from 142 patients with the diagnosis of von Willebrand disease (vWd). Of 114 patients with type I vWd, blood group O was found in 88 (77%), group A in 21 (18%), group B in 5 (4%), and group AB in none (0%), whereas the frequency of these blood groups in the normal population is significantly different (45%, 45%, 7% and 3%, respectively) (P less than .001). Patients with type II or III vWd had ABO blood group frequencies that were not different from the expected distribution. There may be a subset of symptomatic vWd patients with decreased concentrations of structurally normal vWf (vWd, type I) on the basis of blood group O. Some individuals of blood group AB with a genetic defect of vWF may have the diagnosis overlooked because vWF levels are elevated due to blood type.

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