This test includes prothrombin time plus INR and it measures how long it takes your blood to clot. It’s used to monitor the effects of the medication warfarin, and can help identify possible hereditary and clotting disorders. This test does not require fasting. Prothrombin Time (PT) is a blood test used in the evaluation of the extrinsic coagulation system; aid in screening for congenital and acquired deficiencies of factors II, V, VII, X, and fibrinogen. This test is used clinically for the therapeutic monitoring of warfarin (Coumadin®) anticoagulant therapy.