Prothrombin time measured as a ratio- INR. Because the results from the PT test vary from laboratory to laboratory, a INR is calculated. Calcculating it in this formula allows for differences in different laboratories so that the test results can be compared. In most cases the ideal target INR is between 2-3 but for some people at high risk of developing a blood clot the target needs to be higher - 2.5-3.5. If the INR is above target range, it means the blood is clotting too slow, which places a person at risk of bleeding. If it is lower than the target range, it means the blood is clotting quickly, putting the person at risk of developing unwanted clots (Health Navigator, 2020).