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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Hemophilia A is factor VIII deficiency; hemophilia B is factor IX deficiency
- Bleeding is deep: hemarthrosis, muscle hematomas, retroperitoneal bleeding, intracranial hemorrhage
- Labs: prolonged aPTT with normal PT, normal platelet count, and normal bleeding time
- Severe hemophilia presents in infancy or childhood with spontaneous bleeding
- Treatment is factor replacement; emicizumab is prophylaxis for hemophilia A, especially with inhibitors
Overview
Hemophilia A and B are X-linked recessive coagulation factor deficiencies. Factor VIII deficiency is more common. Because platelet function is intact, patients have deep tissue bleeding rather than petechiae-predominant mucocutaneous bleeding. Disease severity correlates with residual factor activity. Recurrent hemarthrosis causes chronic arthropathy. Inhibitor antibodies against infused factor are a major treatment complication.
Epidemiology
Hemophilia affects males primarily, while females may be carriers or rarely symptomatic due to skewed X-inactivation. Hemophilia A is about 4-5 times more common than hemophilia B. Family history may be absent because de novo mutations occur.
Clinical Features
Symptoms
Recurrent painful swollen joints from hemarthrosis
Large muscle hematomas after minor trauma
Prolonged bleeding after circumcision, dental work, surgery, or trauma
Headache, vomiting, neurologic deficit after trauma suggesting intracranial hemorrhage
Neonatal bleeding or bleeding after immunizations in severe disease
Signs
Warm swollen tender joint with reduced range of motion
Large ecchymoses or deep muscle swelling
Compartment syndrome signs: severe pain, tense compartment, neurologic deficit
No petechiae in classic hemophilia; petechiae suggest platelet disorder
Investigations
First-line
PT, aPTT, platelet countIsolated prolonged aPTT with normal PT and platelets
Mixing studyCorrection suggests factor deficiency; failure to correct suggests inhibitor
Factor VIII and IX activityDefines hemophilia A versus B and severity
Second-line
vWF testingDifferentiate hemophilia A from vWD when factor VIII is low or mucosal bleeding is prominent
Inhibitor assayBethesda assay if poor response to factor replacement
Joint imagingUltrasound or MRI for hemarthrosis/arthropathy when needed
Specialist
Genetic testingFamily counseling, carrier testing, prenatal planning, and confirmation in complex cases
Management
National Bleeding Disorders Foundation MASAC guidance and US hemophilia treatment principles1
Acute bleeding
- Give factor replacement promptly for suspected serious bleeding; do not wait for imaging in high-risk bleeding
- Hemophilia A: recombinant factor VIII; hemophilia B: recombinant factor IX
- Suspected intracranial, neck, throat, retroperitoneal, iliopsoas, or compartment bleeding is an emergency
- Avoid IM injections, aspirin, and NSAIDs
2
Mild hemophilia A
- Desmopressin may raise factor VIII in responsive mild hemophilia A
- Desmopressin does not treat hemophilia B
- Tranexamic acid is useful for dental and mucosal bleeding as adjunct
3
Prophylaxis and inhibitors
- Regular factor prophylaxis prevents hemarthrosis in severe disease
- Emicizumab prophylaxis is used for hemophilia A with or without inhibitors
- Bypassing agents are used for inhibitor-associated bleeding under specialist care
Complications
- Chronic arthropathy: Recurrent hemarthrosis destroys joints
- Intracranial hemorrhage: Life-threatening, especially after trauma
- Compartment syndrome: Deep muscle bleeding
- Factor inhibitors: Neutralizing antibodies reduce treatment response
USMLE Step 2 CK Exam Tips
- 1Hemarthrosis + prolonged aPTT + normal platelets = hemophilia
- 2Petechiae point toward platelet disorder, not hemophilia
- 3Hemophilia A = factor VIII; hemophilia B = factor IX
- 4Desmopressin helps mild hemophilia A but not hemophilia B
- 5vWD causes mucosal bleeding and may also prolong aPTT via low factor VIII
- 6Intracranial bleed suspected: give factor immediately before imaging
practicetest your knowledge on hemophilia a & bApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — hematology & oncology and beyond.
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