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, so males with the affected X chromosome are more often clinically affected. Females may be carriers with normal or reduced factor activity and may have bleeding with procedures, menstruation, pregnancy, or childbirth. Factors VIIIa and IXa work together to activate factor X efficiently. This supports a burst of thrombin, which converts fibrinogen to fibrin and stabilizes the platelet plug. When factor VIII or IX is deficient, the reinforcing fibrin mesh is inadequate, so bleeding tends to be delayed, prolonged, and deep. 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. Recurrent painful swelling inside a joint is a stronger clue for hemophilia. Severity depends on baseline factor activity: - Severe: less than 1% activity, or less than 0.01 IU/mL. Spontaneous joint or muscle bleeding may begin in early childhood. - Moderate: 1–5% activity, or 0.01–0.05...