Diagnosis can be difficult. When a healthcare practitioner hears of recurrent nosebleeds, easy bruising, heavy menstrual periods, or longer than usual bleeding after such routine operations as tonsillectomy or tooth extraction, diagnostic tests should be performed to rule out the possibility of von Willebrand disease.

Usually, a person with von Willebrand disease has a parent who has a history of bleeding problems. Typically, a child bruises easily or has prolonged bleeds excessively after a skin cut, tooth extraction, tonsillectomy, or other surgery. A woman may have increased menstrual bleeding. Bleeding may worsen at times. On the other hand, hormonal changes, stress, pregnancy, inflammation, and infections may stimulate the body to increase production of the von Willebrand factor and temporarily improve clot formation.

Laboratory tests may determine that the number of platelets is normal but bleeding time is abnormally long. Bleeding time is the amount of time elapsed before bleeding stops after a small cut is made on the forearm. To make the diagnosis, doctors may order tests that measure the amount of von Willebrand factor in the blood. Because the von Willebrand factor is the protein that carries factor VIII in the blood, the blood level of factor VIII may also be decreased.

Diagnostic signs can include:

• Normal platelet count
• Prolonged bleeding time
• Reduced von Willebrand factor level
• Reduced platelet adhesion may occur
• Reduced or increased platelet aggregation (platelet aggregation test)
• Ristocetin co-factor is reduced