Coagulation Pathway Testing — ORE Part 1 MCQ

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ModerateHuman Disease & Dental ManagementCoagulation Pathway TestingORE Part 1

A patient with a bleeding disorder has a prolonged activated partial thromboplastin time (APTT) but a normal prothrombin time (PT/INR) and normal platelet count. Which coagulation pathway is affected?

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Correct answer: D — Intrinsic pathway

<cite index="10-10">A patient with a prolonged aPTT and a normal PT is considered to have a defect in the intrinsic coagulation pathway.</cite> This pattern is diagnostic because the APTT is sensitive to intrinsic pathway factors (VIII, IX, XI, XII) and common pathway factors, while the PT is sensitive only to extrinsic (Factor VII) and common pathway factors. <cite index="1-1">Normal PTT times require the presence of coagulation factors I, II, V, VIII, IX, X, XI, & XII.</cite> Since the PT (extrinsic and common) is normal, any prolongation in APTT must be due to deficiency in intrinsic-specific factors. Distractor B (extrinsic) is excluded because PT would be prolonged. Distractor C (common pathway) is excluded because both APPT and PT would be prolonged. Distractor D (platelet function) is excluded by normal platelet count. Distractor E (fibrinolytic pathway) is not assessed by routine APPT/PT.

Reference: Blood Coagulation Assays (USPTO patent document 8304205, 2012) and NHS Pathology Laboratory APPT Reference; compatible with SDCEP UK dental guidance on anticoagulation management. https://pathlabs.rlbuht.nhs.uk/APTT.pdf