Which group of coagulation factors are vitamin K-dependent?

• A. II, VII, IX, X
• B. I, II, V, VIII
• C. XI, XII, Fletcher, Fitzgerald
• D. III, IV, V, VI

Answer: (A)

Vitamin K is required to activate certain coagulation factors by enabling gamma-carboxylation, which lets them bind calcium and attach to phospholipid surfaces during clot formation. The factors that undergo this modification are II (prothrombin), VII, IX, and X. Therefore, this group is vitamin K–dependent. Without this carboxylation, these factors are produced but inactive, leading to impaired clotting; drugs like warfarin inhibit the recycling of vitamin K, reducing activity of these factors.

Other listed factors, such as fibrinogen (I) and cofactors V and VIII, do not require vitamin K for their activation, so they’re not vitamin K–dependent groups. Some items mentioned (like tissue factor, calcium as a separate factor, or non-existent factors) aren’t classic coagulation factors, so they don’t fit the vitamin K–dependence pattern.