Hemophilia

Hemophilia A and hemophilia B are inherited deficiencies of secondary hemostasis. Hemophilia A results from deficient factor VIII; hemophilia B results from deficient factor IX. Both are usually X-linked recessive, so males with the affected X chromosome are more often clinically affected. Females may be carriers with normal factor activity, or they may have reduced activity and bleed with procedures, menstruation, pregnancy, or childbirth. Factors VIIIa and IXa work together to activate factor X efficiently. This step supports a burst of thrombin, which converts fibrinogen to fibrin and stabilizes the platelet plug. When factor VIII or IX is deficient, the initial platelet plug may form, but the reinforcing fibrin mesh is inadequate. Bleeding therefore tends to be delayed, prolonged, and deep rather than limited to the skin surface. The characteristic sites are joints, muscles, and internal tissues. Petechiae and frequent superficial mucosal bleeding point more toward a platelet disorder or another primary-hemostasis problem; they are not the classic hemophilia pattern. A patient with hemophilia can still have bruising or a cut, but recurrent painful swelling inside a joint is a...