A 23-year-old man presents with prolonged nose bleeds. He has always noted easy bruising, and ongoing bleeding after minor cuts. There is no prior history of surgery or dental procedures. His hemoglobin is 14.5 g/dL, platelets 200,000/mL, and PT/PPT is normal. Further testing reveals that the bleeding time is elevated; the factor VIII level is reduced, as is the ristocetin cofactor assay.For the above patient with a bleeding disorder, select the most likely diagnosis.

**Core Concept**
The patient's symptoms of prolonged bleeding, easy bruising, and prolonged bleeding time indicate a bleeding disorder. The reduced factor VIII level and ristocetin cofactor assay suggest a deficiency in von Willebrand factor (VWF), a protein essential for platelet adhesion and aggregation.

**Why the Correct Answer is Right**
Von Willebrand disease (VWD) is a genetic disorder characterized by a deficiency or dysfunction of VWF, leading to impaired platelet adhesion and aggregation. The ristocetin cofactor assay is a specific test for VWF function. Factor VIII is also affected in VWD because VWF serves as a carrier protein for factor VIII in the circulation. The patient's normal PT and PTT suggest the absence of a coagulation factor deficiency affecting the intrinsic or common pathway.

**Why Each Wrong Option is Incorrect**
**Option A:** Factor XI deficiency is a bleeding disorder characterized by prolonged PTT, which is not present in this patient.
**Option B:** Hemophilia A is caused by a deficiency of factor VIII, but it typically presents with a more severe bleeding phenotype, including hemarthrosis and muscle bleeding, which are not mentioned in this patient's history.
**Option C:** Platelet disorders, such as thrombocytopenia or platelet dysfunction, would not explain the patient's prolonged bleeding time or the reduced ristocetin cofactor assay.

**Clinical Pearl / High-Yield Fact**
Von Willebrand disease is the most common inherited bleeding disorder, and it can present with a wide range of symptoms, from mild bleeding after minor trauma to severe bleeding after surgery or dental procedures. The ristocetin cofactor assay is a critical test for diagnosing VWD, and it can help differentiate it from other bleeding disorders.

**Correct Answer: C. Von Willebrand disease**

✓ Correct Answer: A. von Willebrand's disease