International normalized ratio (INR)

INR evaluates the safety and how effective warfarin treatment is in preventing blood clots.

International normalized ratio (INR) Overview

Reviewed: April 22, 2014

International normalized ratio (INR) is a measure of how fast blood clots. In addition, INR evaluates how warfarin (Coumadin) is working at thinning the blood.

The normal ranges are the following:

  • No medication: INR should be around 1.0
  • People with atrial Fibrillation have a target INR range of 2.0 to 3.0
  • INR for mechanical valve: 2.5-3.5


Finger stick


Fasting is not required before the test

What the results mean

If you are not taking blood thinning medicines such as warfarin, an INR result above 1.1 means your blood is clotting more
slowly than desired. This may be due to bleeding disorders, liver disease, and low levels of vitamin K.

A result that is too high or too low in someone who is taking warfarin (Coumadin) may be due to
The wrong dose of medicine, drinking alcohol with warfarin, taking certain medicines which may interact with warfarin, and eating certain foods which may change the way warfarin works.