What is the most likely diagnosis for a patient with a family history of bleeders, prolonged bleeding time, normal prothrombin time (PT), prolonged partial thromboplastin time (PTT), and a normal platelet count?

Von Willebrand's Disease

The most likely diagnosis is (e) von Willebrand's disease. This combination of prolonged bleeding time, normal PT, prolonged PTT, and normal platelet count in a patient with a family history of bleeding is pathognomonic for VWD 1.

Diagnostic Reasoning

The coagulation profile provides a clear diagnostic pathway:

• Prolonged bleeding time indicates a defect in primary hemostasis, pointing to either platelet dysfunction or von Willebrand factor deficiency 1

• Normal platelet count (150,000/mm³) immediately excludes thrombocytopenic disorders:

  • Rules out idiopathic thrombocytopenic purpura (ITP), which requires thrombocytopenia and would show normal PTT 1
  • Rules out thrombotic thrombocytopenic purpura (TTP), which presents with thrombocytopenia and is not an inherited disorder 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

Key Distinguishing Feature

The critical differentiating factor is the prolonged bleeding time combined with prolonged PTT 1. This specific pattern distinguishes VWD from the hemophilias:

• Hemophilia A (factor VIII deficiency) and Christmas disease/Hemophilia B (factor IX deficiency) would show prolonged PTT due to their respective factor deficiencies, but bleeding time would be normal because platelet function and von Willebrand factor remain intact 1

• The family history of "bleeders" supports an inherited disorder, consistent with VWD's autosomal dominant inheritance pattern in most cases 2, 3

Pathophysiology

Von Willebrand factor serves dual functions:

• Mediates platelet adhesion to damaged endothelium (primary hemostasis) - explaining the prolonged bleeding time 1
• Serves as a carrier protein for factor VIII - explaining the prolonged PTT due to secondary factor VIII deficiency 1

Confirmatory Testing

While the coagulation profile is highly suggestive, confirmatory testing should include:

• Von Willebrand factor activity (ristocetin cofactor activity) 1
• Von Willebrand factor antigen levels 1
• Factor VIII activity levels 4

Common Pitfall

PT and PTT are not reliable screening tests for VWD - the prolonged bleeding time is the key distinguishing feature that separates VWD from the hemophilias 1. Many clinicians may overlook ordering bleeding time in the modern era, but this case demonstrates its diagnostic value.