Von Willebrand's Disease (Answer: e)
The most likely diagnosis is von Willebrand's disease (VWD), given the combination of prolonged bleeding time, normal PT, prolonged PTT, normal platelet count, and family history of bleeding.
Diagnostic Reasoning
The coagulation profile in this case provides a clear diagnostic pattern:
- Prolonged bleeding time indicates a defect in primary hemostasis (platelet function or von Willebrand factor) 1
- Normal PT excludes deficiencies in the extrinsic pathway (factors VII, X, V, II, and fibrinogen) 1
- Prolonged PTT indicates a deficiency in the intrinsic pathway (factors VIII, IX, XI, or XII) 1
- Normal platelet count (150,000/mm³) excludes thrombocytopenic disorders like ITP or TTP 1
Why Von Willebrand's Disease
VWD is the only disorder among the options that produces both a prolonged bleeding time and prolonged PTT with a normal platelet count 1. This occurs because:
- Von Willebrand factor is essential for platelet adhesion, so its deficiency causes prolonged bleeding time 2
- Von Willebrand factor also serves as a carrier protein for factor VIII, so VWD leads to secondary factor VIII deficiency and prolonged PTT 2
- VWD is the most common diagnosed bleeding disorder, particularly in children with family history of bleeding 3
Why Not the Other Options
Hemophilia A (option c) and Christmas disease/Hemophilia B (option d):
- Both would show prolonged PTT due to factor VIII or IX deficiency 4
- However, bleeding time would be normal because platelet function and von Willebrand factor are intact 1, 2
- These are X-linked recessive disorders, making them less likely in a general "family of bleeders" presentation 4
Idiopathic Thrombocytopenic Purpura (option a):
- Would show thrombocytopenia (platelet count <100,000/mm³), not a normal count 1
- PTT would be normal 1
Thrombotic Thrombocytopenic Purpura (option b):
- Would show thrombocytopenia and is not an inherited bleeding disorder 1
- This is an acquired condition, not consistent with family history 1
Clinical Pitfalls to Avoid
Important caveat: PT and PTT are not reliable screening tests for VWD 1. The PTT may be normal in mild VWD if factor VIII levels are adequate. The prolonged bleeding time is the key distinguishing feature here 1.
Confirmatory testing should include:
- Von Willebrand factor antigen levels
- Von Willebrand factor activity (ristocetin cofactor activity)
- Factor VIII activity levels 2
The family history of "bleeders" strongly supports an inherited disorder, and VWD accounts for the majority of inherited bleeding disorders in the general population 3, 2.