what is a inr test
International Normalized Ratio (INR) is a blood test that measures the time it takes for blood to clot. Learn more about what INR test results mean for you. International Normalized Ratio (INR) is a blood test that measures the time it takes for blood to clot. This test is usually administered to people taking anticoagulants or blood thinners. INR Levels. The lower the INR number, the shorter it takes for blood to clot and the greater risk you have for blood clots.