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Oral Surgery · single question

Von Willebrand disease (associated with Factor VIII) — which is the BEST diagnostic test?

  1. PT/INR
  2. Bleeding time alone
  3. Platelet count
  4. PTT (activated partial thromboplastin time) — evaluates the intrinsic pathway
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Correct answer: D. PTT (activated partial thromboplastin time) — evaluates the intrinsic pathway

  • A. PT/INR tests the EXTRINSIC pathway (Factor VII) and common pathway — used for warfarin monitoring and Factor VII deficiency.
  • B. Bleeding time tests platelet function (adhesion/aggregation) and is prolonged in VWD, but PTT is the more specific coagulation test.
  • C. Platelet count would be normal in most VWD cases — VWD is a quantitative/qualitative platelet-adhesion defect, but platelet count remains normal.
  • D. Correct. Von Willebrand disease affects Factor VIII (von Willebrand factor carries Factor VIII and protects it from degradation). Factor VIII is part of the INTRINSIC COAGULATION PATHWAY. The PTT (aPTT) tests factors of the intrinsic pathway (XII, XI, IX, VIII) and the common pathway (X, V, II, I). In VWD, PTT is prolonged. Also: Hemophilia A (Factor VIII) and Hemophilia B (Factor IX) both prolong PTT.

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