A 32-year-old woman presents with a lifelong history of easy bruising and epistaxis. Laboratory investigations show normal platelet count, normal PT, prolonged aPTT, and normal bleeding time. Which feature best distinguishes von Willebrand disease from hemophilia A in this clinical scenario?

Question

Accepted Answer

B. von Willebrand disease shows abnormal ristocetin-induced platelet aggregation (RIPA), whereas hemophilia A shows normal RIPA. ## Distinguishing von Willebrand Disease from Hemophilia A

### Key Laboratory Differences

**Key Point:** The **ristocetin-induced platelet aggregation (RIPA) test** is the single best discriminator between von Willebrand disease (vWD) and hemophilia A. In vWD, RIPA is abnormal (reduced or absent) because von Willebrand factor (vWF) is deficient or dysfunctional. In hemophilia A, RIPA is **normal** because the platelet adhesion pathway is intact — only factor VIII is deficient.

### Comparative Features

| Feature | von Willebrand Disease | Hemophilia A |
|---------|------------------------|---------------|
| **Platelet count** | Normal | Normal |
| **Bleeding time** | Prolonged (Type 1, 3) or normal (Type 2) | Normal |
| **aPTT** | Prolonged | Prolonged |
| **PT** | Normal | Normal |
| **RIPA** | **Abnormal (reduced/absent)** | **Normal** |
| **vWF antigen (vWF:Ag)** | Low/absent | Normal |
| **vWF activity (vWF:RCo)** | Low/absent | Normal |
| **Factor VIII** | Low (parallel to vWF) | Low/absent (independent of vWF) |
| **Bleeding pattern** | Mucosal (epistaxis, menorrhagia) | Joint/muscle (hemarthroses, hematomas) |

### Pathophysiology

**Clinical Pearl:** von Willebrand factor serves **two critical functions**:
1. **Platelet adhesion** to subendothelium (via GPIb receptor)
2. **Carrier protein** for factor VIII (protects from degradation)

In vWD, both functions are impaired → abnormal RIPA + low factor VIII.
In hemophilia A, only factor VIII synthesis is defective → normal RIPA + normal vWF.

**High-Yield:** RIPA is **pathognomonic for vWD** — it is abnormal in vWD and normal in hemophilia A, making it the gold-standard discriminator.

### Why Bleeding Time is Not the Best Discriminator

Bleeding time is **prolonged in Type 1 and Type 3 vWD** but **normal in Type 2 vWD** (qualitative defect). Hemophilia A always has normal bleeding time. However, bleeding time is **not standardized** and has fallen out of favor in modern practice — RIPA is more reliable and specific.

Answer

A. Factor VIII levels are always <1% in von Willebrand disease but variable in hemophilia A

Answer

C. Platelet count is reduced in von Willebrand disease but normal in hemophilia A

Answer

D. Bleeding time is prolonged in von Willebrand disease but normal in hemophilia A

A 32-year-old woman presents with a lifelong history of easy bruising and epistaxis. Laboratory investigations show normal platelet count, normal PT, prolonged aPTT, and normal bleeding time. Which feature best distinguishes von Willebrand disease from hemophilia A in this clinical scenario?

Explanation

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