Prothrombin is a plasma protein produced by the liver. A prothrombin time test measures how long it takes for the blood to clot. Clotting is caused by a series of clotting factors activating each other, including the conversion of prothrombin to thrombin.
What might a high result mean?
An increased prothrombin time indicates your blood is taking longer to form a clot. If you are not taking anticoagulant drugs and your prothrombin time is prolonged, additional testing may be necessary to determine the cause.