Prevalence of von Willebrand disease in children: a multiethnic study.

OBJECTIVE: Von Willebrand disease (vWD) was thought to be a rare disorder until a recent survey reported a prevalence of 0.8% in an ethnically homogenous community in northern Italy. The purpose of this study was to determine the prevalence of vWD in an ethnically heterogenous population. METHODS: Von Willebrand factor (vWF) was measured by the ristocetin cofactor method in 600 healthy children, aged 2 to 18 years, seen for routine school physical examinations in a three-state region. Personal and family bleeding symptoms were determined by questionnaire. The diagnosis of vWD required a personal history of bleeding symptoms, an abnormal vWF activity concentration, and a family history of at least one immediate family member with bleeding symptoms. RESULTS: A total of 315 subjects were white, 212 were black, 16 were Hispanic, 10 were from other groups, and 47 were biracial. Eight subjects (four black, four white) met the criteria for vWD, for a prevalence of 1.3%. Seven subjects with vWD had blood group O (mean vWF = 32 U/dl; range, 10 to 42 U/dl), and one had blood group A (vWF = 41 U/dl). Children who had blood group O had significantly (p < 0.001) lower vWF activities (median, 83 U/dl, range, 43 to 162 U/dl) than those from non-O blood groups (median, 98 U/dl; range, 51 to 190 U/dl). There were no significant differences in vWF activity by ethnicity. The vWF activity was significantly (p < 0.02) greater for boys than girls in both blood groups. CONCLUSION: Von Willebrand disease is the most common congenital hemostatic disorder; its high prevalence is not limited to one ethnic group.

Relative value of diagnostic studies for von Willebrand disease.

Laboratory tests recommended to screen patients with mucosal bleeding for hemostatic disorders generally include determinations of prothrombin time, partial thromboplastin time, platelet count, and bleeding time. To determine the best tests to identify patients with von Willebrand disease (vWD), we reviewed the laboratory studies of 24 children with vWD and performed receiver operating characteristic analysis on the diagnostic studies. The vWD disease diagnostic tests included determinations of vWF activity (ristocetin cofactor activity), vWF factor antigen, and factor VIII procoagulant (VIII:c). The diagnosis of vWD required the presence of a personal and family history of bleeding symptoms and a documented abnormality of vWF activity or vWF antigen. vWF activity, vWF antigen, factor VIII:c and blood type were determined in 104 symptom-free children. There were no differences between patients and normal subjects for age, gender, or blood type. The bleeding time was abnormal in 43%, the partial thromboplastin time was abnormal in 25%, and either one or both were abnormal in 58% of the patients. The vWF activity, vWF antigen, and factor VIII:c were abnormal in 79%, 58%, and 33%, respectively. Receiver-operated-characteristic analysis showed the vWF activity to be superior to either the vWF antigen or factor VIII:c in establishing the diagnosis of vWD. The combination of the activity, bleeding time, and partial thromboplastin time successfully identified 92% of the patients as abnormal. Determination of vWF activity should be included routinely in the evaluation of hemostasis in children with symptomatic disease.