Prothrombin time: A test that is done to gauge the integrity of part of the blood clotting process. Prothrombin time is commonly used to screen for bleeding disorders as well as to monitor the accuracy of blood-thinning treatment (anticoagulation) with drugs such as warfarin (brand names: Coumadin, Panwarfin, Sofarin). It measures the time needed for clot formation after thromboplastin and calcium are added to plasma. Familiarly known as pro time.
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