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Warfarin and Vitamin K - Topic Overview

How vitamin K and warfarin affect your risks and your test results

To find out how well warfarin is working, you will get blood tests to measure how long it takes for your blood to clot. Your lab results are called your Prothrombin Time (PT) and International Normalized Ratio (INR) values. You may just hear about your INR.

Your INR needs to be in a safe range-not too high and not too low. Vitamin K can change how warfarin works, which changes your INR.

  • Vitamin K lowers your INR values. The lower your INR, the less time it takes for your blood to clot. A low INR means that warfarin isn't working well enough to prevent a dangerous blood clot.
  • Warfarin raises your INR values. The higher your INR, the more time it takes for your blood to clot. A high INR means that warfarin is working too well, so you bleed more quickly and easily. This can be dangerous.

Keeping your warfarin and vitamin K intake steady every day helps keep you in a safe INR range.

This information is produced and provided by the National Cancer Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National Cancer Institute via the Internet web site at http:// cancer .gov or call 1-800-4-CANCER.

WebMD Medical Reference from Healthwise

Last Updated: October 31, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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