Why would Vitamin K lower the INR?

Why would Vitamin K lower the INR?

• A. Because it increases synthesis of clotting factors, shortening clotting time
• B. It decreases vitamin C levels
• C. It dilates blood vessels
• D. It increases platelet production

Answer: (A)

INR reflects how long it takes blood to clot through the vitamin K–dependent clotting factors II, VII, IX, and X. Vitamin K is essential for these factors to become functional. When vitamin K is available, the liver can produce more of these active factors, speeding up the clotting process and shortening the clotting time, which lowers the INR. This is why giving vitamin K reverses or reduces an elevated INR, especially in someone on warfarin. The other ideas don’t fit because vitamin C doesn’t regulate these factors, dilating vessels doesn’t change the coagulation cascade measured by the INR, and platelet production affects primary hemostasis rather than the vitamin K–dependent clotting factors in plasma.

INR reflects how long it takes blood to clot through the vitamin K–dependent clotting factors II, VII, IX, and X. Vitamin K is essential for these factors to become functional. When vitamin K is available, the liver can produce more of these active factors, speeding up the clotting process and shortening the clotting time, which lowers the INR. This is why giving vitamin K reverses or reduces an elevated INR, especially in someone on warfarin. The other ideas don’t fit because vitamin C doesn’t regulate these factors, dilating vessels doesn’t change the coagulation cascade measured by the INR, and platelet production affects primary hemostasis rather than the vitamin K–dependent clotting factors in plasma.