Prothrombin time

The prothrombin time (PT) — along with its derived measures of prothrombin ratio (PR) and international normalized ratio (INR) — are assays evaluating the extrinsic pathway of coagulation. This test is also called "ProTime INR" and "PT/INR". They are used to determine the clotting tendency of blood, in the measure of warfarin dosage, liver damage, and vitamin K status. PT measures factors I (fibrinogen), II (prothrombin), V, VII, and X. It is used in conjunction with the activated partial thromboplastin time (aPTT) which measures the intrinsic pathway and common pathway.