| Description: |
Factor IX is a vitamin K-dependent clotting factor which is synthesized in the liver. Congenital deficiency of factor IX (hemophilia B, Christmas disease) is transmitted as an X-linked recessive trait. Clinically, hemophilia B is indistinguishable from hemophilia A (factor VIII deficiency). Severe hemophilia B (<1% activity) is characterized by delayed bleeding after injury and spontaneous deep bleeding (e.g., retroperitoneum, muscles, joints, hematuria). Acquired deficiency of factor IX occurs with liver disease, warfarin therapy, and vitamin K deficiency. Less Inhibitors (inhibiting antibodies) to factor IX may arise as an alloimmune complication of factor replacement in severely deficient patients. Autoantibodies to factor IX are rare. The best screening test for factor IX deficiency is the aPTT, which is sensitive to factor IX levels of <30%. |
