A normal INR is 0.8 to 1.1 for people not taking blood thinners and 2.0 to 3.0 for people taking warfarin and other blood-thinning drugs, according to MedlinePlus. INR stands for international normalized ratio.
Laboratories often use INR to report the results of the prothrombin time test. The PT test measures how long it takes for the plasma in the blood to clot. In someone who doesn't take blood thinners, an INR of 1.1 or greater indicates the blood is not clotting quickly enough. Causes of slow clotting time include liver disease, vitamin K deficiency, bleeding disorders and a condition called disseminated intravascular coagulation.
The desired INR range is not the same for every person taking blood thinners, states MedlinePlus. Although many doctors advise their patients to maintain an INR of 2.0 to 3.0, it's not unusual for a doctor to set a different goal based on a patient's medical history. If someone taking a blood thinner has an INR outside the desired range, his doctor might have to adjust the dosage of the blood-thinning medication. Some food and drugs also interfere with the way blood thinners work. An INR of less than 2.0 means someone is at risk of a blood clot, while an INR above 3.0 indicates the person may have an increased risk of bleeding.