Medicine & USMLE

Hemophilia A

  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 A is a X-linked recessive bleeding disorder caused by a deficiency in factor 8. Patients with hemophilia A present with easy bruising and bleeding, including bleeding into the joint spaces and muscles. Lab testing in patients with hemophilia A will reveal decreased levels of factor 8 and an increased PTT. Treatment includes desmopressin for milder cases, although severe cases will require factor 8 replacement.

Key Points

  • Hemophilia A
    • Pathogenesis
      • Deficiency of Factor VIII
        • Leads to inadequate generation of thrombin (Factor IIa) and improper coagulation of blood
        • Inhibits intrinsic coagulation cascade
    • 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 VIII 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
      • ddAVP (desmopressin)
        • Increases endogenous factor VIII, since vWF is a carrier that stabilizes circulating Factor VIII
        • Used for mild cases
      • Recombinant Factor VIII replacement
        • Used for severe cases