A 28-year-old woman with a lifelong history of easy bruising and menorrhagia is found to have a normal platelet count, normal PT, and prolonged aPTT that corrects with normal plasma. A bleeding time is normal. Which single feature best distinguishes von Willebrand disease from hemophilia A in this patient?

## Distinguishing von Willebrand Disease from Hemophilia A ### Clinical Context This patient has a prolonged aPTT that corrects with normal plasma, a **normal bleeding time**, normal platelet count, and normal PT — along with mucosal bleeding (menorrhagia) and easy bruising. The stem explicitly states the bleeding time is **normal**, which is the key laboratory clue here. ### Comparison Table | Feature | von Willebrand Disease | Hemophilia A | | --- | --- | --- | | **Inheritance** | Autosomal dominant (Type 1, 2) or recessive (Type 3) | X-linked recessive | | **Bleeding time** | Often prolonged (platelet dysfunction via vWF) | Normal | | **Mucosal bleeding** | Very common (primary hemostasis defect) | Less common; deep tissue bleeding predominates | | **Menorrhagia** | Very common | Rare | | **aPTT** | Prolonged (low Factor VIII) | Prolonged (low Factor VIII) | | **vWF antigen** | Low or abnormal | Normal | | **Platelet count** | Normal | Normal | ### Key Point: **Mucosal bleeding and menorrhagia** are the single best clinical discriminators of vWD from hemophilia A in this scenario. vWD causes a defect in **primary hemostasis** (platelet plug formation via vWF-GPIb interaction), leading to mucosal-type bleeding — epistaxis, menorrhagia, gingival bleeding, and easy bruising. Hemophilia A causes a defect in **secondary hemostasis** (Factor VIII deficiency), leading to deep tissue bleeding — hemarthroses, muscle hematomas — with mucosal bleeding being far less prominent. ### High-Yield (Harrison's Principles of Internal Medicine): vWD is the most common inherited bleeding disorder and classically presents with **mucocutaneous bleeding** in women of reproductive age. Hemophilia A, being X-linked recessive, is rare in females and presents predominantly with deep-tissue hemorrhage rather than mucosal symptoms. ### Clinical Pearl: The normal bleeding time in this stem is consistent with certain subtypes of vWD (e.g., Type 2N, which affects vWF's binding to Factor VIII rather than platelet adhesion) or mild Type 1 vWD where the bleeding time may be borderline. Regardless, the **clinical phenotype of mucosal bleeding and menorrhagia** remains the best single distinguishing feature from hemophilia A in the context of this question. ### Why Other Options Are Less Discriminatory: - **Autosomal inheritance (Option C):** While vWD is autosomal and hemophilia A is X-linked, inheritance pattern alone requires a detailed family history and is not a single "feature" observable in this patient's presentation. Mucosal bleeding is directly observable and clinically more discriminating in this vignette. - **Normal bleeding time with prolonged aPTT (Option B):** This pattern is actually more characteristic of **hemophilia A** (normal primary hemostasis, defective secondary hemostasis), not vWD. This option would favor hemophilia A. - **Correction of aPTT by mixing (Option D):** Both vWD and hemophilia A correct with normal plasma (which supplies both vWF and Factor VIII). This is not discriminatory between the two conditions.