Hi, I had my aortic valve replacement 18 months ago and am doing OK on warfarin. My INR fluctuates a lot, ranging from 1.9 to 6 on the same doseage of warfarin. so it needs constant adjustment. I am also on Eltroxin for hypothyroid treatment and my cardio says that is what causes the fluctuations. When my thyroid is overactive the INR becomes high and when it is underactive the INR becomes low. My thyroid function is a bit erratic. I want to know if there is anybody in this site who has thryroid problems and is on anti coagulation therapy?