Medical Emergencies · single question
A patient with Von Willebrand disease is planning an extraction. Which lab test is MOST important to evaluate?
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Correct answer: C. PTT (partial thromboplastin time)
Von Willebrand disease (vWD) primarily affects platelet adhesion (vWF is required for platelet-to-collagen binding) AND Factor VIII levels (vWF carries Factor VIII in plasma). The PTT measures the intrinsic coagulation pathway (factors XII, XI, IX, VIII) and is prolonged in vWD due to low Factor VIII. Additionally, bleeding time and ristocetin cofactor activity are specific tests for vWD. For dental pre-extraction assessment, PTT is the standard coagulation screening test for vWD patients.
- A. ❌ INR reflects warfarin anticoagulation therapy — not relevant to vWD.
- B. ❌ PT measures the extrinsic pathway (Factors VII, X, V, II, fibrinogen) — not affected in vWD.
- C. ✅ CORRECT – PTT is prolonged in vWD because low vWF leads to low Factor VIII, which is part of the intrinsic pathway measured by PTT.
- D. ❌ Platelet count is usually normal in vWD — the problem is platelet function (adhesion), not count.
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