Which of the following bleeding disorders is characterized by a normal bleeding time but prolonged prothrombin time (PT)?

Explanation

## Coagulation Pathway Defects and Bleeding Time **Key Point:** Bleeding time reflects platelet function and primary hemostasis (platelet plug formation), while PT reflects the extrinsic coagulation pathway (Factors II, V, VII, X). ### Bleeding Time vs. PT | Parameter | Reflects | Abnormal In | |-----------|----------|-------------| | **Bleeding Time** | Platelet number & function, vWF | Thrombocytopenia, platelet dysfunction, von Willebrand disease | | **PT** | Extrinsic pathway (Factors II, V, VII, X) | Factor V, VII, X, II deficiencies; vitamin K deficiency; warfarin therapy | | **aPTT** | Intrinsic pathway (Factors VIII, IX, XI, XII) | Factor VIII, IX, XI, XII deficiencies; heparin therapy | ### Factor V Deficiency **High-Yield:** Factor V is unique — it participates in BOTH the extrinsic pathway (via tissue factor-Factor VII complex) AND the common pathway (prothrombin activation). Therefore: - **PT is prolonged** (extrinsic pathway defect) - **aPTT is prolonged** (common pathway defect) - **Bleeding time is NORMAL** (platelet function intact) **Clinical Pearl:** Factor V deficiency is rare (1:1,000,000). Patients present with mucosal bleeding, hemarthrosis, and hematoma — similar to hemophilia but with a different coagulation profile. **Warning:** Do not confuse Factor V deficiency with Factor VIII deficiency (hemophilia A), which has normal PT but prolonged aPTT. ### Why Other Options Are Wrong - **von Willebrand disease:** Prolonged bleeding time (platelet dysfunction/adhesion defect), normal or slightly prolonged PT - **Platelet function disorder:** Prolonged bleeding time (platelet dysfunction), normal PT - **Thrombocytopenia:** Prolonged bleeding time (low platelet count), normal PT [cite:Harrison 21e Ch 139]