INR, abbreviated as International Normalized Ratio, is a test that measures the blood clotting time in patients who are taking blood thinners, such as warfarin. Sometimes, doctors may refer to INR with other synonyms, such as prothrombin time (PT) and coagulation time. INR is also known as normalized ratio (NR), which compares the blood's clotting time to the normal clotting time. An INR value of 1.0 is normal, whereas values above 3.0 indicate that the blood takes longer to clot. Monitoring INR levels is crucial in patients who take blood thinners to prevent blood clots, which can lead to heart attacks, strokes, or other life-threatening blood vessel blockages.