In a patient taking warfarin, what is the primary reason to maintain a consistent intake of vitamin K–containing foods?

• A. To prevent fluctuations in blood pressure
• B. To prevent fluctuations in platelet count
• C. To prevent fluctuations in INR
• D. To prevent fluctuations in heart rate

Answer: (C)

Warfarin’s effect depends on how much vitamin K is available to activate the clotting factors. Vitamin K–dependent factors II, VII, IX, and X need vitamin K to function, and warfarin works by inhibiting this pathway. If dietary vitamin K intake varies, the production of these clotting factors can swing, causing the INR to move up or down. Keeping vitamin K intake consistent minimizes these swings, helping keep the INR within the therapeutic range so the anticoagulant effect stays steady. This isn’t about blood pressure, platelet counts, or heart rate—the key issue is maintaining stable INR to balance bleeding and clotting risk.