Question

Consider the following statements about Factor VIII (AHF), which is involved in the coagulation mechanism of haemostasis:
1. Only in extrinsic pathway
2. Only in intrinsic pathway
3. In common pathway
Which of these statements is/are correct?

• A. 1 only
• B. 2 only
• C. 1 and 3
• D. 2 and 3

Hint:

Factor VIII pairs with factor IX in the intrinsic pathway.

Answer 1

The Correct Option is B

Step 1: Understanding the Question.
We need to place Factor VIII, also called antihemophilic factor, in the correct part of the classic coagulation cascade.

Step 2: Key Concept.
The classic cascade splits clotting into an intrinsic pathway (factors XII, XI, IX, VIII), an extrinsic pathway (factor VII and tissue factor), and a common pathway that starts once factor X is activated (factors X, V, II or thrombin, and I or fibrinogen).

Step 3: Detailed Explanation.
Factor VIII works as a cofactor for activated factor IX, and together they form the tenase complex that activates factor X. This role places Factor VIII firmly inside the intrinsic pathway. It has no role in the extrinsic pathway, which depends on tissue factor and factor VII instead. Because the intrinsic and common pathways are taught as separate stages, Factor VIII itself is not counted as a common pathway factor even though its job feeds into the start of the common pathway. This is exactly why a person missing Factor VIII, as in Hemophilia A, shows a prolonged activated partial thromboplastin time (which tests the intrinsic pathway) but a normal prothrombin time (which tests the extrinsic pathway).

Step 4: Final Answer.
Factor VIII acts only in the intrinsic pathway, so statement 2 alone is correct.