Which coagulation factors are vitamin K dependent?

• A. Factors II, VII, IX, X (and proteins C and S)
• B. Factors I, II, V, X
• C. Factors VIII, IX, XI
• D. Factors II, VII, IX, X

Answer: (D)

Vitamin K enables a posttranslational modification called gamma-carboxylation on certain coagulation factors, which allows them to bind calcium and associate with phospholipid surfaces during the clotting process. The coagulation factors that require this vitamin K–dependent modification are II (prothrombin), VII, IX, and X. When vitamin K is deficient or when its action is blocked (as with warfarin), these factors are undercarboxylated and less active, leading to reduced coagulation. It’s also worth noting that while proteins C and S are vitamin K–dependent, they are anticoagulant regulators, not coagulation factors, so they aren’t included when listing the vitamin K–dependent coagulation factors.