The von Willebrand factor is found in plasma, platelets, and the walls of blood vessels. Platelets are cells that are made in the bone marrow and circulate in the bloodstream and help blood clot. When the von Willebrand factor is missing or defective, platelets cannot adhere to the vessel wall at the site of an injury. As a result, bleeding does not stop as quickly as it should.
Platelets are cells that circulate in the bloodstream and help blood clot. The blood usually contains about 140,000 to 440,000 platelets per microliter (140 × 109 to 440 × 109 per liter). When the platelet count falls below about 50,000 platelets per microliter of blood (50 × 109 per liter), bleeding can occur even after relatively minor injury. The most serious risk of bleeding, however, generally does not occur until the platelet count falls below 10,000 to 20,000 platelets per microliter of blood (10 ×109 to 20 × 109 per liter). At these very low levels, bleeding may occur without any recognized injury.
There are three main types of von Willebrand disease, all of which are inherited. The types differ on the degree of deficiency of the factor. People with the greatest deficiency have a higher risk of bleeding.
Less commonly, people can develop von Willebrand disease without inheriting an abnormal gene, and this condition is called acquired von Willebrand disease. For example, people with certain cancers or autoimmune disorders sometimes form antibodies to von Willebrand factor. In other people with certain heart and blood vessel diseases, von Willebrand factor is broken down and becomes deficient. In both cases, as in inherited von Willebrand disease, the result is increased bleeding.
Often, a person with von Willebrand disease has a parent who has a history of bleeding problems. Typically, a child bruises easily or bleeds excessively after a cut, tooth extraction, or surgery. A young woman may have increased menstrual bleeding. Bleeding may worsen at times. On the other hand, hormonal changes, pregnancy, inflammation, and infections may stimulate the body to increase production of von Willebrand factor and temporarily improve the capacity of platelets to stick to the blood vessel wall and stop bleeding.
In most forms of von Willebrand disease, laboratory tests typically show that the platelet count is normal. One standard test of blood clotting (the prothrombin time [PT]) is usually normal while another standard test (partial thromboplastin time [PTT]) is usually prolonged.
Doctors usually order tests that measure the amount of von Willebrand factor in the blood and determine how well the von Willebrand factor functions. Because von Willebrand factor is the protein that carries an important clotting factor (factor VIII) in the blood, the level of factor VIII in the blood may also be decreased (resulting in a prolonged PTT test).
Many people with von Willebrand disease never need treatment.
If excessive bleeding occurs, a transfusion of concentrated blood clotting factors containing von Willebrand factor (intermediate-purity factor VIII concentrates or recombinant von Willebrand factor) may be given.
For some mild forms of von Willebrand disease, drug treatment with desmopressin may be given to increase the amount of von Willebrand factor long enough for surgery or dental procedures to be done without transfusions. Sometimes drugs that promote clotting, such as epsilon aminocaproic acid or tranexamic acid, are used alone or with desmopressin.
For women with heavy menstrual bleeding due to von Willebrand disease, a brief period of treatment with tranexamic acid by mouth may decrease bleeding.