These last two points have almost the same answer.
The ranges are decided by a committee. They look at research that has been done, decide how well done it is etc and then vote.
Not only would they wait to announce their findings but this meeting is almost a year behind schedule. The committee has many members (including the co-chair) from Ontario, Canada. They were scheduled to meet last year just as the SARS outbreak took place and travel in and out of Toronto was restricted. So the meeting was put off for almost a year.
Keep in mind
1. These are guidelines - not laws
2. It is hard to keep any individual within the guidelines more than about 60% of the time
3. It is not only how far out of the guidelines that you are but how long you stay out.
At my clinic we routinely test about every 4 to 5 weeks for people who have been on warfarin for a long time.
The results
1. A minor bleed about every 18 patient months
2. A major bleed about every 33 patient years
3. A clotting episode about every 100 patient years.
Most INRs below 8 result in no bleeding
I take action when the INR gets more than 0.2 units low
I take action when the INR gets above 5
If you test more frequently or used tighter guidelines what can you hope to achieve?
Would there be a noticable improvement if the guidelines said 2.6 to 3.4?
Could you get the minor bleeding rate down to every 15 months?
Could you get the major bleeding rate down to every 30 years? 25 years?
Could you get the clotting rate down to every 90 years?
Would these be an improvement in your life when weighed against daily testing?
Blindness, amputations, and dialysis occur at high rates in diabetics yet how hard is it to get diabetics to test their blood sugar even once a day? Is it likely that people with heart valves would do much better than diabetics?
That is why I don't think we need to know day-to-day variations in the INR, or have tighter guidelines. I just do not think that these will result in major improvements in the quality of life.
Read the responses to the thread with the questionaire about how peoples lives were changed and how they live with warfarin. Those who responded seemed to be doing fairly well with what we have now.
I think that the greatest improvement in the lives of the members would be to reduce the risk when warfarin needs to be discontinued.
