International normalised ratio (INR) test

Key facts The international normalised ratio (INR) blood test tells you how long it takes for your blood to clot. It is used to test clotting times in people taking warfarin (a medicine used to treat and prevent blood clots). Your doctor will use your INR result to work out what dose of warfarin you should take. International normalised ratio (INR) test What is the international normalised ratio blood test? The international normalised ratio (INR) blood test tells you how long it takes for your blood to clot. A test called the prothrombin time (PT) actually measures how quickly your