MS-0553

An 80-year-old patient is initiated on warfarin after being diagnosed with atrial fibrillation. The patient has a medical history of a metallic heart valve.

The patient is informed that INR levels will be used to monitor the effects of warfarin. INR is a ratio of the value during warfarin treatment to the normal value, which is used to measure a specific aspect of clotting.

What is the value that is utilized during this monitoring process?