Vitamin K deficiency affects which of the following factors?

• A. Factor II and VII
• B. Factor VII and IX
• C. Factor II, VII, IX, and X
• D. Factor VIII and IX

Answer: (C)

Vitamin K is required for gamma-carboxylation of several coagulation factors, which lets them bind calcium and assemble on phospholipid surfaces to form active clotting complexes. The factors that depend on this modification are II (prothrombin), VII, IX, and X; without vitamin K, these factors become undercarboxylated and lose activity, leading to impaired coagulation. Among the options, the set that includes II, VII, IX, and X is the correct one. Factor VIII, while important in the intrinsic pathway as a cofactor with IX, does not require gamma-carboxylation by vitamin K, so its activity isn’t directly reduced by vitamin K deficiency.