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Sékouba Sidimé: vWD vs Hemophilia A – The Classic USMLE Step 1 trap in Hematology
Jun 2, 2026, 19:42

Sékouba Sidimé: vWD vs Hemophilia A – The Classic USMLE Step 1 trap in Hematology

Sékouba Sidimé, Internal Medicine Physician, shared a post on LinkedIn:

vWD vs Hemophilia A – The No. 1 USMLE Step 1 trap in Hematology

One lab result tells them apart.Here’s what you need to know:

von Willebrand Disease

  • Prolonged aPTT, prolonged Bleeding time, decreased Ristocetin 
  • Female with a family history and mucocutaneous bleeding
  • Treatment: Desmopressin (DDAVP)

Hemophilia A

  • Prolonged aPTT , Bleeding time normal, Ristocetin normal
  • Male with hemarthroses
  • Treatment: Factor VIII replacement

The key:

vWF carries Factor VIII — decreased vWF results in secondary reduction of Factor VIII.

That’s why vWD affects both aPTT AND bleeding time.

Hemophilia A affects aPTT only.

If the examiner mentions Ristocetin then think vWD. Every time.”

Sékouba Sidimé

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