The prothrombin time blood test is used to test how quickly a person's blood clots. This time is an indicator of the quality and amount of clotting factors present, according to WebMD.
Blood coagulation time may be tested when patients are on routine blood thinning medications, such as warfarin or heparin. The test allows the physician to adjust the dosage based on whether the time is too high or too low, explains WebMD.
Another reason doctors may order the test is when they suspect a patient has a liver disorder. The prothrombin time test and liver enzymes are used to diagnose end-stage liver disease and determine the eligibility of a patient for a transplant, according to Mayo Clinic.