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Question 303
Physiology → Haematology
Classification
Question
SSBAOptions
Explanation
Haemophilia A is an X-linked recessive factor VIII deficiency affecting the intrinsic pathway. It does not interfere with initial haemostasis due to vascular closure; therefore bleeding time remains normal, while factor VIII deficiency increases clotting time and subsequent bleeding may persist.
Option Validity
A) Factor VIII deficiency affects the intrinsic rather than the extrinsic pathway. Initial vascular closure is unaffected, so bleeding time remains normal.
B) A normal bleeding time is compatible with haemophilia A, but the pathway assignment is incorrect. Haemophilia A affects the intrinsic pathway.
C) Bleeding time is not prolonged in haemophilia A. The abnormality lies in coagulation after initial vascular haemostasis rather than in the initial bleeding-time mechanism.
E) The pathway is correctly identified as intrinsic, but factor VIII deficiency increases rather than reduces clotting time. The coagulation defect therefore delays effective clot formation.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Haemophilia A, p.72.