An INR test, otherwise known as a PT test, measures how long it takes blood to clot, according to WebMD. INR stands for international normalized ratio, which indicates a standard way to notate the results of a PT test, otherwise known as a prothrombin time test. INR standardizes how test results read, even if blood tests come back from different labs. These blood tests indicate bleeding problems or whether blood-thinning medications work properly.
Doctors may use a PT test to find the cause of abnormal bleeding, check the overall effects of warfarin, test for hemophilia, determine levels of vitamin K in the blood or check to see if surgeon can perform a procedure that causes bleeding, notes WebMD. This test measures the levels of five different clotting factors in the blood stream. Prothrombin time could run longer due to blood thinners, low levels of clotting factors, clotting inhibitors and a change in activity of clotting factors.
Too much of some clotting factors could cause excessive clotting, while too little may cause excessive bleeding, says Lab Tests Online. Doctors may prescribe warfarin and other blood-thinning medications for those who have an irregular heartbeat, artificial heart valves, deep vein thrombosis or a pulmonary embolism. Blood tests that doctors may order alongside INR or PT tests include a platelet count, thrombin time, fibrinogen and coagulation factor test.