Anticoagulation therapy is monitored by the PT-INR test. PT stand for “prothrombin time” and is a measure of how quickly blood clots. The test works by mixing the blood with a reagent that causes it to clot. Because different reagents are used, different PT tests can have different results. In order to correct for this, the result of the PT test is converted to a standardized value, known as INR. INR stands for “International Normalized Ratio”; it enables results of a PT test using one reagent to be compared to other PT tests utilizing other reagents.
A person with a normal clotting time will have an INR value close to one. The higher the value, the longer it takes for the blood to clot. People with values that are less than one, the risk for clotting is high. A person taking an anticoagulant drug, like warfarin should have a INR somewhere between 2 and 4. If the INR is above 5, there is an increased risk for bleeding.
