Sometimes a malfunction of the body's immune system causes it to make antibodies that attack the person's own tissues (autoantibodies) instead of attacking foreign or dangerous substances. Such disorders are called autoimmune disorders.
Circulating anticoagulants are usually autoantibodies that develop spontaneously (on their own and without a known cause) and decrease the activity of a specific clotting factor (a protein that helps the blood clot) and, therefore, cause excessive bleeding (see also Overview of Blood Clotting Disorders). For example, the immune system may produce an autoantibody against clotting factor VIII or factor V. These antibodies are called circulating anticoagulants because they travel (circulate) in the bloodstream.
Circulating anticoagulants usually cause excessive bleeding. However, some people with certain types of circulating anticoagulants develop blood clots within an artery or vein instead of excessive bleeding. Such blood clots may cut off blood flow, causing redness and swelling as well as damage to the tissue supplied by the blood vessel.
Antibodies to factor VIII develop in about 30% of people with severe hemophilia A. The antibodies develop as a complication of repeated exposure to normal factor VIII molecules that are given to treat the hemophilia. Similarly, people with severe hemophilia B can develop antibodies to factor IX, although this occurs in only about 3% of people.
Factor VIII autoantibodies also arise occasionally in people without hemophilia. For example, factor VIII anticoagulants may develop in women who have just given birth or in people who have an autoimmune disorder, such as rheumatoid arthritis or systemic lupus erythematosus. Sometimes, older people who have no apparent underlying disorder develop factor VIII anticoagulants.
People with a factor VIII anticoagulant can develop life-threatening bleeding.
Blood tests are done, including measurement of the amount of factor VIII or the amount of factor IX.
In postpartum women, the autoantibodies may disappear spontaneously. Otherwise, people without hemophilia may be given drugs such as cyclophosphamide, corticosteroids, or rituximab to suppress autoantibody production. People with antibodies to factor VIII who are bleeding may also be given activated factor VII.
Several new drugs are available or being tested for use to control bleeding in people with hemophilia and isoantibodies to factor VIII or factor IX.