The coagulation factors referred to as 'vitamin K-dependent' are

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

Answer: (C)

Vitamin K is required for the post-translational modification of certain coagulation proteins by gamma-carboxylating glutamate residues, which enables calcium binding and proper activity on phospholipid surfaces. The factors that depend on this vitamin are prothrombin (factor II), factor VII, factor IX, and factor X. Without this carboxylation, these proteins cannot participate effectively in the coagulation cascade, leading to impaired thrombin generation and longer clotting times. The other factors listed—fibrinogen (I), V, VIII, XI, XII, and XIII—do not require vitamin K for activation, so they are not vitamin K–dependent. The odd names included aren’t recognized coagulation factors and thus don’t belong in this group.