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Question 331
Physiology → Haematology
Classification
Question
SSBAOptions
Explanation
Factor VIII deficiency affects the intrinsic coagulation pathway in haemophilia A. Initial vascular closure is unaffected, so initial haemostasis and bleeding time may remain normal, but defective coagulation allows subsequent persistent oozing.
Option Validity
A) Haemophilia A results from factor VIII deficiency rather than defective platelet formation. Initial platelet and vascular haemostasis can therefore still occur.
B) Factor XIII with calcium stabilises the fibrin mesh, but excessive factor XIII activity is not the defect in haemophilia A. The disorder results from factor VIII deficiency.
D) Tissue thromboplastin initiates the extrinsic pathway, whereas haemophilia A affects the intrinsic pathway. Failure of extrinsic initiation therefore does not explain these findings.
E) Initial vascular closure is unaffected and bleeding time remains normal. The abnormality becomes evident through defective subsequent coagulation and persistent bleeding.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Haemophilia A, p.72.