Hemophilia: Inherited Secondary Hemostasis Deficiencies
Hemophilias are a group of hereditary bleeding disorders characterized by a deficiency or dysfunction of specific clotting factors in the intrinsic coagulation cascade. Because these conditions represent primary defects in secondary hemostasis, patients have normal platelet plugs but cannot form a stable fibrin mesh. This manifests as delayed, deep-tissue bleeding rather than superficial mucocutaneous petechiae.
1. High-Yield Classification and Genetics
The three primary types of hemophilia are distinguished by the specific factor missing and their distinct genetic inheritance patterns:
- Hemophilia A (Classic Hemophilia): X-linked recessive deficiency of functional Factor VIII. It is the most common type, accounting for approximately 85% of cases.
- Hemophilia B (Christmas Disease): X-linked recessive deficiency of functional Factor IX. Clinically indistinguishable from Hemophilia A, it requires specific quantitative factor assays to differentiate.
- Hemophilia C: Autosomal recessive deficiency of Factor XI. It is seen primarily in individuals of Ashkenazi Jewish descent and typically presents with a milder bleeding phenotype.
2. Clinical Manifestations
The severity of symptoms correlates closely with the level of residual clotting factor activity. Classic presentation clues include:
| Clinical Feature | Pathophysiology and Presentation Details |
|---|---|
| Hemarthrosis | Bleeding directly into weight-bearing joints (knees, elbows, ankles) triggered by minimal or unnoted trauma. Erythematous, warm, and painful joint swelling occurs, leading to chronic hemophilic arthropathy and joint destruction over time. |
| Deep Tissue Hematomas | Bleeding within large muscle groups (iliopsoas, gastrocnemius). Can lead to nerve compression or compartment syndrome. |
| Neonatal Bleeding | Prolonged, oozing hemorrhage following routine neonatal procedures, such as circumcision or umbilical cord separation. |
| Post-Surgical Hemorrhage | Characteristically delayed bleeding after dental extractions or minor surgeries. Initial platelet plug handles immediate hemostasis, but the plug breaks down without fibrin stabilization. |
3. Diagnostic Laboratory Evaluation
A high-yield coagulation profile is essential to isolate hemophilia from primary hemostatic or common-pathway defects:
- Activated Partial Thromboplastin Time (aPTT): Characteristically prolonged because Factors VIII, IX, and XI are core components of the intrinsic pathway.
- Prothrombin Time (PT / INR): Entirely normal, as the extrinsic pathway remains fully functional.
- Platelet Count & Bleeding Time: Entirely normal, demonstrating that primary hemostasis mechanics are uncompromised.
- 1:1 Mixing Study: Patient plasma is mixed with normal pooled plasma. Because hemophilia involves a simple quantitative deficiency, the aPTT corrects completely back to normal limits. Failure to correct points toward an acquired factor inhibitor (autoantibody).