Definition of Prothrombin time

Prothrombin time: A clotting test, the prothrombin time is done to test the integrity of part of the clotting scheme. The prothrombin time is commonly used as a method of monitoring the accuracy of blood thinning treatment (anticoagulation) with warfarin (Coumadin). Familiarly called the "pro time," the test is the time needed for clot formation after a substance called thromboplastin (+ calcium) has been added to plasma.

Prothrombin is a coagulation (clotting) factor needed for the normal clotting of blood.

There is a cascade of biochemical events that leads to the formation of the final clot. In this cascade, prothrombin is a precursor to thrombin. Because prothrombin comes before thrombin, it is called prothrombin.