Von Willebrand Disease (VWD) is defined as an inherited bleeding disorder that is caused by deficiency or dysfunction of von Willebrand factor (VWF), a plasma protein that mediates the initial adhesion of platelets at sites of vascular injury and also binds and stabilizes blood clotting factor VIII (FVIII) in the circulation. The most severe forms of VWD are usually easy to diagnose (obvious hemorrhagic symptoms and major VWF deficiency), whereas the mild forms of the disease are still difficult to confirm. It is indeed reported that about 1% of the population carry mild biological VWF deficiency without any bleeding tendency and any "actual disease". On the contrary, some patients with severe bleeding history can carry a true VWF abnormality, well-confirmed by genetic studies, without any VWF deficiency when evaluated with standard biological methods, such as Ristocetin Cofactor activity (VWF:RCo). However, in these patients, the use of alternative methods, such as PFA-100 (Platelet Fonction Analyzer-100), the study of Factor VIII (FVIII:C) to VWF (FVIII:C/VWF) ratio or the evaluation of VWF activity using more specialized methods such as VWF:CB (VWF-Collagen Binding) assay can detect the VWF deficiency and possible hemorrhagic predisposition.

In this project, the investigators plan to assess the performance of VWF:CB in the diagnosis of VWF deficiency in patients with unexplained bleeding history.

Inclusion Criteria:

• Patient with bleeding history sent to the Hemophilia Treatment Center in Dijon or Nantes University Hospital with abnormal bleeding score (>3 in men and >5 in women
• Patient who has provided a signed consent to participate at this study and for blood sampling
• Affiliation with French social security system

Non-Inclusion Criteria:

• Minors will not be included in the study.
• On-going pregnancy and postpartum period (3 months after delivery)
• Substitutive treatment with coagulation factor concentrates or desmopressin administration within 10 days before sampling.
• Ongoing infectious or inflammatory disease that can modify VWF levels.
• Diagnosis of obvious hemostasis disorder

This study plans to enroll 200 patients (100 per Center) in a 2-year period. The recruitment will occur in standard consultation activity of the 2 Hemostasis Centers of Dijon and Nantes. As each Center carries out about 1200 consultations/year, this projection appears as feasible, since a majority of them are induced by hemorrhagic profile. Such a number of patients will allow reliable statistical analysis.