Coagulation Factors

von Willebrand factor is responsible for helping platelets stick to the injured blood vessel wall. A blood clot then occurs around platelets at the site of injury. A deficiency or abnormality in von Willebrand factor can cause von Willebrand disease, an inherited bleeding disorder. It is associated with a secondary decrease in factor VIII concentration, as von Willebrand factor also binds to and stabilizes factor VIII in the blood stream. While von Willebrand factor may be used with coagulation factors if an inherited factor deficiency is suspected, it is usually considered separately because it is associated with platelets and not part of the classic coagulation cascade.

The severity of bleeding depends on the individual, the degree of abnormal factor concentration and/or function as well as which factor is deficient. Those who have a missing factor or one with very low activity will have more severe manifestations of the disease. Patients with one normal gene copy and one altered gene copy (heterozygous) will tend to have less severe bleeding than those with two altered copies (homozygous). Patients with a deficiency of factor XII are usually asymptomatic. This rare factor deficiency causes abnormal PTT results but is not associated with increased bleeding. It may even be associated with a mild tendency to form clots!