The international normalized ratio, or INR, measures the length of time it takes for blood to clot, according to eMedTV. The World Health Organization, or WHO, introduced this test to monitor the safety of patients taking blood-thinning medications, especially warfarin.
Health care providers use the INR to maintain the warfarin response within a recommended range, explains the American Association for Clinical Chemistry. Warfarin works by inhibiting a formation of blood clots. The goal of using INR is to maintain a balance between preventing the clotting of blood and causing excessive blood loss. It takes careful monitoring to maintain this balance in a patient using warfarin. The INR is vital in adjusting the dose of warfarin to get the clotting time within the desired range.
A physician can order the test when a patient is on warfarin, or when a patient is showing signs of abnormal clotting or excessive bleeding, states the American Association for Clinical Chemistry. The doctor can also order the test before performing a surgical procedure that has a high risk of blood loss. The test is also useful when a patient has a history of bleeding, such as easy bruising or frequent nose bleeding. The INR returns results in seconds, which the doctor compares with normal values. A higher-than-normal ratio indicates blood is taking too long to clot.