INR Blood Test
If you are taking an anticoagulant (an oral blood-thinning medicine), you will have to undergo a laboratory test called the international normalized ratio (INR). This blood test is used to make sure that the amount of your anticoagulant medicine in your blood is within a normal level.
During an INR test, a blood sample is taken and the amount of time it takes for your blood to clot is compared to an average. This resulting number is the international normalized ratio. The longer it takes the blood to clot, the higher the INR value. However, if your INR is too high, you may have an increased risk of uncontrollable bleeding. If the value is too low, you may be at risk for developing a blood clot or stroke.
(Click INR for a closer look at what this ratio is, how it is calculated, and why it is important that your INR be neither too high nor too low.)