How Is Range Determined?

[temp69]

This has been flummoxing me. How do "they" determine your range. I was told I had to be between 2.5 and 3.5. some are between 3 and 4. some between 2 and 3, etc. what gives?

 

[Ross]

Nothing is set in stone. A Doctor can modify the range as needed, but the basic guideline suggestions can be found here:
http://www.aafp.org/afp/990201ap/635.html Table 1

 

[DrAllan]

Range is determined by a combination of various factors. Each of the indications for ACT has a different rate of clotting and risk of embolism. Just looking at valves, there is a difference in valves in the mitral position as compared to the aortic position. Combinations of valves have different risk ratios. These ‘ratios’ are determined from measuring the complication rates in patients and trying to account for the level of ACT they had. For those of you who have INR fluctuations, one may wonder how to extrapolate that to an assessment of risk. Nevertheless there are some clear trends. With this in mind then finding that certain levels of INR change the risks gives an indication of the range that provides a margin of safety. Add to this the medical maxim, “I’ve always done it this way, or that is what my teachers taught me” one winds up with accepted ranges. If one actually tries to find scientific articles that explore the methodology, they are few and far between, old and have a relatively small sample of patients. One of the mantras of this sight leans toward tolerating higher levels, which do reduce the risk of clotting without a significant increase in bleeding episodes.

Bottom line, some science, some rumor and some witchcraft

 

[Natanni]

My husband had overall heart enlargement, left ventricle enlargement (and thickening) as well as an ejection fraction of 45% at the time of his aortic valve replacement. Upon discharge from the hospital post AVR, his INR range was 2.5-3.5 due to atrial fib and an ejection fraction of 35%. At 10 months post op with a normal size heart EF 53% and a consistant normal sinus rhythm his cardio at the Mayo wanted to lowed his INR to 2-3.