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

This question tests where Factor VIII, the antihemophilic factor, fits inside the coagulation cascade.

1. 1 only (extrinsic pathway): Wrong, because the extrinsic pathway runs on tissue factor and factor VII, not factor VIII.
2. 2 only (intrinsic pathway): Correct. Factor VIII teams up with activated factor IX to form the tenase complex, which then switches on factor X. This job belongs to the intrinsic pathway.
3. 1 and 3: Wrong on both counts since factor VIII plays no direct part in the extrinsic or common pathway.
4. 2 and 3: Half right, half wrong. Factor VIII does belong to the intrinsic pathway, but it is not classed as a common pathway factor, since the common pathway begins only after factor X is switched on.

The clinical proof of this grouping is Hemophilia A, where a missing factor VIII prolongs the activated partial thromboplastin time (an intrinsic pathway test) while the prothrombin time (an extrinsic pathway test) stays normal.

Let's summarize:

• Factor VIII pairs with factor IX to activate factor X, a job that belongs to the intrinsic pathway.
• It plays no role in the extrinsic pathway and is not itself labeled a common pathway factor.

So statement 2 alone is correct.