INR – a short guide

What is INR?

INR means International Normalised Ratio (INR) and is a method of measuring how fast the blood clots. In a person not taking warfarin, the INR value will be one. The higher the INR the longer it takes for the blood to clot, for instance an INR of two means that it takes the blood twice as long to form clots compared to somebody not taking warfarin. Your doctor or specialist nurse will tell you what your target INR range is as it will depend on why warfarin has been prescribed.

What is INR testing?

To help measure the INR we use an INR machine which calculates how long it takes for the blood to clot and works out the ratio giving the INR result. INR testing involves obtaining a small sample of blood, usually a finger prick and applying a drop of blood to a test strip. INR testing is important as this determines what dose of warfarin is needed which the warfarin clinic will manage.