Medicine & USMLE

Hemophilia B

  1. Common Pathway of Coagulation
  2. Extrinsic Pathway of Coagulation
  3. Intrinsic Pathway of Coagulation
  4. Hemophilia A
  5. Hemophilia B
  6. Hemophilia C
  7. Factor V Leiden
  8. Antithrombin-3 Deficiency


Hemophilia B is an inherited blood clotting disorder caused by a deficiency in clotting factor 9. As an X-linked recessive disease, it primarily affects male patients. Patients with hemophilia B present with bleeding. A diagnosis is made by detecting deficient factor 9, but may be supplemented by the finding of an elevated PTT.

Key Points

  • Hemophilia B
    • Also known as Christmas Disease
    • Pathogenesis
      • Deficiency of Factor IX
        • Leads to inadequate generation of thrombin (Factor IIa) and improper coagulation of blood
    • Genetics
      • XLR inheritance
        • Almost exclusively affects males
    • Presentation
      • Clinical symptoms indistinguishable from other hemophilias
      • Bleeding
        • Hemarthrosis - bleeding into joints
        • Intramuscular hemorrhage
        • Easy bruising
        • Bleeding after trauma or surgery (e.g. dental procedure)
    • Diagnosis
      • Definitive: Factor IX levels
      • Elevated PTT
        • Due to inhibited intrinsic coagulation pathway
      • Normal PT
        • Extrinsic (tissue factor) pathway is unaffected
      • Normal Bleeding Time
        • Platelet plug formation (primary hemostasis is unaffected)
    • Treatment
      • Recombinant Factor IX concentrate