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At a Glance
Why Get Tested?
A prothrombin time (PT) is a test used to help detect and diagnose a bleeding disorder or excessive clotting disorder; the international normalized ratio (INR) is calculated from a PT result and is used to monitor how well the blood-thinning medication (anticoagulant) warfarin (Coumadin®) is working to prevent blood clots.
When to Get Tested?
When you are taking warfarin or when you have unexplained or prolonged bleeding or inappropriate blood clotting
A blood sample drawn from a vein in your arm; sometimes blood from a fingerstick
Test Preparation Needed?
None needed, although if you are receiving anticoagulant therapy, the specimen should be collected before taking your daily dose.