A normal prothrombin time is 11 to 13.5 seconds for patients who are not taking anticoagulants, according to MedlinePlus. Prothrombin time is the number of seconds it takes for the blood plasma to clot. An elevated prothrombin time means the blood is clotting more slowly than it should.
Doctors usually order a prothrombin time test to monitor patients during treatment with warfarin, an anticoagulant, explains MedlinePlus. Prothrombin time tests may also be ordered to look for causes of abnormal bruising or bleeding, check liver function or look for a bleeding disorder. Liver disease and low levels of vitamin K may cause patients who are not taking warfarin to have an elevated prothrombin time.