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Hemophilia USMLE Notes & Mnemonics contains all the high-yield points you need to know.


  • Hemophilia: A group of hereditary genetic disorders that impair the body’s ability to control blood clotting. (Ref)


  • Hemophilia A: Deficiency of factor VIII (8)
  • Hemophilia B: Deficiency of factor IX (9), also known as Christmas disease


  • X-linked recessive: Primarily affects males
  • Female carriers: May have some degree of factor deficiency


  • Deficiency in clotting factors leads to impaired secondary hemostasis
  • Does not affect platelet plug formation (primary hemostasis)

Clinical Features:

  • Hemarthrosis: Bleeding into joints, especially knees, ankles, and elbows
  • Easy bruising
  • Prolonged bleeding: After trauma or surgery
  • Spontaneous bleeding: In severe cases


  • Prolonged aPTT: Normal PT/INR
  • Low factor VIII or IX: Assayed to distinguish between Hemophilia A and B
  • Normal bleeding time: Because primary hemostasis is intact
  • Genetic testing: Can identify carriers and affected individuals


  • Recombinant factor VIII or IX: Mainstay for Hemophilia A and B respectively
  • Desmopressin (DDAVP): Can raise factor VIII levels in mild Hemophilia A
  • Antifibrinolytics: Such as tranexamic acid for mucosal bleeding
  • Avoid NSAIDs: Due to bleeding risk


  • Regular infusions of clotting factors to prevent bleeding


  • Hemophilic arthropathy: Chronic joint disease due to recurrent bleeding
  • Inhibitor development: Antibodies against factor concentrates
  • Transfusion-transmitted infections: Less common with recombinant factors


  • A for Eight: Hemophilia A is a deficiency of factor VIII
  • B for IX: Hemophilia B is a deficiency of factor IX

High-Yield Facts:

  • Queen Victoria: Was a carrier of Hemophilia B, spreading it to the royal families of Europe
  • Carrier mothers: 50% chance of passing the gene to sons, daughters have a 50% chance of being carriers
  • Intracranial hemorrhage: A leading cause of death in hemophiliacs

Chart: Laboratory Findings in Hemophilia

TestHemophilia AHemophilia BNormal
Bleeding TimeNormalNormalNormal
Factor VIII levelDecreasedNormalNormal
Factor IX levelNormalDecreasedNormal

Additional Considerations:

  • Gene therapy: An emerging treatment modality
  • Prenatal diagnosis: For known carrier mothers
  • Newer agents: Emicizumab, a bispecific monoclonal antibody, can bridge factor IXa and X to restore the function of missing factor VIII

Note: On the USMLE, be prepared to identify clinical scenarios suggestive of Hemophilia and understand the basic principles of management, including the avoidance of medications that can exacerbate bleeding.

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