PROTHROMBIN TIME PT/INR THIS TEST MEASURES HOW LONG IT TAKES BLOOD TO CLOT. PT/INR IS ALSO USED TO DIAGNOSE THE PROBLEM AND TO SEE IF THE MEDICATION IS WORKING. AN ABNORMAL PT IS OFTEN CAUSED BY TREATMENT WITH BLOOD THINNERS OR LIVER DISEASE OR INJURY. PT TEST IS IMPORTANT TEST BECAUSE IT CHECKS ON FIVE DIFFERENT BLOOD CLOTTING FACTORS. BLOOD CLOTTING FACTORS ARE NEEDED FOR BLOOD TO CLOT (COAGULATION). THIS TEST IS OFTEN DONE TO CHECK FOR BLEEDING PROBLEMS OR THE CHANCE FOR TOO MUCH BLEEDING.