INR, or international normalized ratio, is another way to report prothrombin time, states MedlinePlus. Prothrombin time measures how long it takes for blood plasma to clot.
A normal INR level ranges from 0.8 to 1.1 in people who are not taking blood thinners, reports MedlinePlus. Someone who takes warfarin, a blood-thinning medication, may need to maintain a higher INR of 2.0 to 3.0. An INR of greater than 1.1 in a patient who is not taking blood thinners indicates undesirably slow blood clotting; this can be caused by issues such as liver disease, vitamin K deficiency or problems with the clotting mechanism of the blood.