Prothrombin is a protein produced by your liver. It is one of many factors in your blood that help it to clot appropriately. A prothrombin time test measures how quickly your blood clots. Sometimes called a PT or pro time test, a prothrombin time test uses a sample of your blood.
The test is indicated for monitoring patients on the blood thinner cumadin. A drug that is used in patients with mechanical heart valves, patients with chronic AFib, and also patients with blood clots to reduce the risk of further clotting and stroke.