OP do you not regularly have an INR test done to determine the clotting response in your blood. I too have AFIB and I have the test done regularly. The interval time is dependent on the last INR factor. I have on occasion done two tests per week as the INR factor was outside the acceptable range. My normal testing interval is one to three weeks. In the event I am having any kind of invasive procedure, the coumadin is terminated for a period of time that is usually 5 days in advance of the procedure and several days after. If the procedure is a very serious the coumadin is replaced with heparin or a heparin derivative, self administered for 5 days before the surgery. The anti-coagulation effect of the heparin can be reversed with an injection. Not so with the rat poison (coumadin)!