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Question 340
Physiology → Haematology
Classification
Question
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An anticoagulant produces an immediate effect by potentiating irreversible complex formation between antithrombin and activated serine-protease coagulation factors. Which laboratory pattern is most consistent with this mechanism?
Question Stem
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Options
A
APTT is used for monitoring, while the effect on PT is minimal
B
PT alone is used for monitoring because only factor VII is affected
C
Neither APTT nor PT can reflect its anticoagulant action
D
Bleeding time is the principal measure because coagulation factors are unaffected
E
ESR is used because the principal action is on erythrocyte sedimentation
Explanation
Heparin has an immediate anticoagulant effect by potentiating formation of irreversible complexes between antithrombin and activated serine-protease coagulation factors. APTT is used to monitor heparin treatment, while its effect on PT is minimal.
Option Validity
B) PT assesses the extrinsic and common pathways, but heparin is monitored using APTT and has minimal effects on PT.
C) APTT can be used to monitor heparin treatment. The statement that neither test reflects its effect is therefore incorrect.
D) Bleeding time primarily reflects platelet function and vascular contraction rather than the anticoagulant effect on the coagulation pathway described here.
E) ESR measures erythrocyte sedimentation and is not used to monitor the anticoagulant action of heparin.
Further Reading
Saxena R. Textbook for MRCOG-1. Chapter 3: Physiology – Haematology. p.72.