The correct answer is C. Factor VII
Vitamin K is synthesized by the intestinal flora; therefore long- term treatment with broad-spectrum antibiotics can induce a vitamin K deficiency by clearing intestinal flora. Vitamin K is a necessary cofactor for hepatic production of clotting factors II, VII, IX, and X and proteins C and S. Factor VII has the shortest half-life of all clotting factors (4–6 hours), which is why the prothrombin time is prolonged first in vitamin K deficiency.
Answer A is incorrect. Factor II requires vita- min K as a cofactor, and early factor II deficiency would result in prolongation of pro- thrombin time and partial thromboplastin time. However, the half-life of factor II is 42– 72 hours, and thus it would not be deficient before factor VII is deficient.
Answer B is incorrect. Vitamin K is not required for factor V synthesis and would not be deficient in this patient.
Answer D is incorrect. Factor VIII is not a vitamin K dependent clotting factor.
Answer E is incorrect. Factor XI is not a vitamin K dependent clotting factor.
Answer F is incorrect. Factor XII is not a vitamin K dependent clotting factor.