prothrombin time measurement (EFO_0008390) is quantification of the clotting tendency of blood plasma following the addition of tissue factor. Prothrombin time requires the presence of factors I, II, V, VII, and X. It measures the extrinsic pathway of coagulation and can be used in conjunction with the activated partial thromboplastin time (aPTT) which measures the intrinsic pathway. It is used as a screening test and can be affected by vitamin K deficiency, liver disease, warfarin therapy or intestinal problems. Also known as: International normalized ratio of prothrombin time measurement, PT/INR measurement, ProTime INR measurement.