A laboratory blood test called the international normalized ratio (INR) is used for people who are taking blood-thinning medications, such as warfarin (Coumadin®, Jantoven®). The INR value measures how long it takes for the blood to clot.
A healthy person who is not taking a blood-thinning medicine will typically have an INR of about 1. However, people taking oral blood-thinning medicines have a higher INR value. As the dose is increased, a person's INR should also increase.
If the INR is out of range, it could lead to potentially serious complications. For example, if a person's INR is too high, it can lead to uncontrollable bleeding; an INR that is too low may increase your risk for a stroke.
(For more information, click INR. This full-length article provides detailed information on how the INR value is calculated, how often this test is performed, and the specific values that are considered an ideal INR range.)