Hope this helps:
The PT (Prothrombin Time) is the amount of time needed to form a clot. It is measured in seconds. The INR (International Normalized Ratio) is a special mathematical calculation of the PT, used to monitor the effect of oral anticoagulants. For the patient getting PO therapy with Coumadin (Warfarin), the therapeutic range of the INR is 2.0 to 3.0. If the pt has a mechanical heart valve the therapeutic range of the INR is 2.5-3.5.
Although the test done includes BOTH the PT and INR, it is the INR that we use most often, because it is standardized across the world.
We monitor the PT/INR to determine the effect of anticoagulant therapy. If it is too low, ther is a risk for thrombus (clot) formation. If the level is too high, there is a risk for hemorrhage. In a normal person who does not need anticoagulants, the levels should be the PT is 10-14 seconds, and the INR should be 1.00-1.30.
In a pt with an MI, you would want the INR to be 2.0-3.0.
Hope this helps.