Excellent discussion by some very knowledgeable folks. My DW has AFIB and I have an artificial mitral valve. So I/we need to be very aware of our PT/INR. AFIB INR is to be between 2.0 to 3.0 and artificial valve recipients is to be between 2.5-3.5. For me, I cannot use Pradaxa and other non-testing blood thinners. So I must test usually once a month unless I stray out of that range. Too high is not a big problem, but too low and I'm in trouble. In fact, I suffered a stroke when my INR dropped to 1.9 because of a mistake in my dosage by my family doctor. Fortunately, all I lost was about one hour of my memory.....very, very lucky. Since then my cardiologist monitors my PT/INR. Good luck to all you Coumadin users. ;)