What is Prothrombin Time?

Prothrombin time is a medical test that measures the time it takes for blood to clot, according to WebMD. It is used to assess whether or not a patient has bleeding problems and if medicine administered to prevent blood clots is working as expected.

Prothrombin is a type of chemical called a blood clotting factor, and it is made by the liver, states WebMD. Prothrombin time can be increased by blood-thinning medicine, low levels or absence of blood clotting factors, alterations in the activity of blood clotting factors, increased use of blood clotting factors, and substances that inhibit blood clotting factors. Medical conditions, such as liver disease or injury, can also affect prothrombin time.