There are many factors in the blood that are involved in the forming of clots to stop bleeding. A child with hemophilia is missing, or has a low supply of, one of the factors needed in order for the blood to clot. Two common factors that affect blood clotting are factor VIII and factor IX.
Hemophilia is classified by its level of severity. Hemophilia may be mild, moderate, or severe, depending on the level of the blood clotting factors in the blood.
The three main forms of hemophilia include the following:
- Hemophilia A--caused by a lack of the blood clotting factor VIII; approximately 85 percent of hemophiliacs have type A disease.
- Hemophilia B--caused by a deficiency of factor IX.
- Hemophilia C--some doctors use this term to refer to a lack of clotting factor XI
- von Willebrand disease--a part of the factor VIII molecule known as von Willebrand factor or ristocetin cofactor is reduced. The von Willebrand factor involves helping the platelets (blood cells that control bleeding) attach to the lining of a vein or artery. This missing factor results in prolonged bleeding time because the platelets are unable to attach to the wall of the vessel and form a plug to stop the bleeding. This disease is similar to hemophilia, but is not usually called by this name. It is more common and usually milder than hemophilia.