I have been taking Warfarin for almost a year. I started with 7.5 mg per day and blood tests twice a week. After 2 weeks I was backed down to 5 mg a day and 7.5 on monday and friday, then down to just 5 mg a day after about a month. I have been on 5mg a day for almost 10 months now and have a home INR machine. I take my INR every monday and have been pretty steady at 2.4 to 2.8 with every test. For the last 5 or 6 weeks my INR has been jumping around again ranging from 1.8 to 3.3 and I can't figure out why. I have basically the same diet and the same activity levels so I just can't understand why the results are changing now. I am scheduled for an ablation in about 4 weeks and the bouncing INR could stop it from happening. Two weeks ago the reading was 3.2 so I only took 2.5mg that day. Last week back to 2.6 and then this monday 3.3 so I skipped my pill on tuesday. I've got to get this INR in line or it could stop the ablation and then it could take 3 to 6 months to get it scheduled again. Sometimes I wonder if it could be the change in weather? Could the cold weather effect the INR reading?