PFA-100 Prolonged Diagnosis — ORE Part 1 MCQ

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HardHuman Disease & Dental ManagementPFA-100 Prolonged DiagnosisORE Part 1

A patient reports mucocutaneous bleeding. Their PFA-100 closure time is prolonged, but platelet count, PT/INR and APTT are within their laboratory reference ranges. Which disorder category is most likely?

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Correct answer: A — Von Willebrand or platelet-function disorder

The best answer is **A**. PFA-100 closure time is a high-shear test of primary haemostasis, relying on von Willebrand factor-mediated platelet adhesion and normal platelet function. Thus, a prolonged result with a normal platelet count and normal PT/INR and APTT points to von Willebrand disease or a qualitative platelet-function disorder. Factor VIII deficiency (haemophilia A) and factor IX deficiency (haemophilia B) are intrinsic-pathway defects and would usually prolong APTT. Factor VII deficiency is an extrinsic-pathway defect and would prolong PT/INR. Excess vitamin K antagonist effect reduces vitamin K-dependent coagulation factors and typically prolongs PT/INR. The normal routine coagulation results therefore support a primary, rather than secondary, haemostatic defect.

Reference: Harrison P, Robinson MSC, Mackie IJ, et al. Performance of the platelet function analyser PFA-100 in testing abnormalities of primary haemostasis. Blood Coagulation & Fibrinolysis. 1999. https://pubmed.ncbi.nlm.nih.gov/10070832/