The goal of this prospective cohort is to identified specific biological patterns in patients with a bleeding of unknown cause and to study the specific mechanisms of the bleeding disorder for each subset of patients.

Patients with bleeding of unknown cause are included. At baseline, blood will be drawn to evaluate the hemostatic profile. Findings are compared to a control group of healthy individuals. Patients and controls are followed for 3 years.

Inclusion Criteria:

• Man with ISTH BAT>3. If the calculated score includes a surgical bleeding, then two other items of the score should be >0
• Woman with ISTH BAT >5 points. If the calculated score includes a surgical or a postpartum bleeding, then two other items of the score should be >0

Exclusion Criteria:

• Ongoing pregnancy
• Intake of antithrombotic treatment or non-steroidal anti-inflammatory drugs for least 10 days at time of blood collection
• Intake of antifibrinolytic or blood product administration (factor concentrate, frozen fresh plasma, prothrombin complex concentrate) for least 14 days before blood collection
• Active cancer (defined as cancer diagnosis within the last five years or treatment within the two last years before study inclusion)
• Active autoimmune disease
• Active chronic inflammatory disease
• Severe liver disease (cirrhosis > Child A)
• Renal insufficiency stage 3
• Active or recent infection (within the last 30 days)
• Recent hospitalization (<3 months)
• Recent surgery (<3 months)
• Recent trauma requiring medical intervention (<3 months)

Women and men aged 16-65 years who have been diagnosed as patients with bleeding of unknown cause Women and men aged 16-65 years without bleeding tendency