The prothrombin time (PT) is a test that helps evaluate a person’s ability to appropriately form blood clots. The international normalized ratio or INR is a calculation based on results of a PT that is used to monitor individuals who are being treated with the blood-thinning medication (anticoagulant) warfarin (Coumadin).
When you are taking warfarin or when you have unexplained or prolonged bleeding or inappropriate blood clotting, this test is ordered.
Test Normal Ranges
Prothrombin time (PT) 11-14 seconds
Partial thromboplastin time (PTT) 25-35 seconds
International normalized ratio (INR) 0.8 to 1.2
