An alternate name for the INR blood test is PT test, notes WebMD. INR stands for international normalized ratio, and PT stands for prothrombin time. There are two names for the test because the INR test is simply a way to standardize the PT test, despite the method used.
The INR standard allows doctors to read and understand the test results no matter what lab they come from, states WebMD. An INR or PT test is used to find out how long it takes a person's blood to clot. Doctors order the test to detect bleeding problems and make sure that prescribed blood thinners are effectively preventing blood clots from forming.