Acquired Inhibitors of Coagulation Factors

Acquired inhibitors of coagulation factors are antibodies that inhibit the production or clearance of a coagulation factor. The most common autoantibodies occur against factor VIII. The incidence is 1.4 cases per million per year. This condition is termed acquired hemophilia A (AHA). Common etiologies for acquired inhibitors are postpartum, autoimmune disease, malignancy, and drug induced. However, 50% are idiopathic. Acquired inhibitors occur in a bimodal distribution because of some patients being associated with pregnancy and others in older age. The median age of onset is 77 years. Patients typically present with bleeding, such as postoperative bleeding, postpartum hemorrhage, melena, hematuria, and bleeding into skin or muscle. In contrast to congenital hemophilia, hemarthroses are uncommon. Bleeding in AHA may be more severe than congenital hemophilia despite similar factor levels. Autoantibodies to other clotting factors may be associated with a variety of disorders and present with variable clinical findings.