This study was proposed and carried out in response to the concern that an testing monthly was expensive and inconvenient. Other research had previously shown either that there wasn't a 'statistically significant' difference between shorter and longer intervals, at least in terms of outcomes, or that it was difficult to detect the difference. Where it is flawed is that it demonstrates an unfamiliarity with anti-coagulation, and a misapprehension, one that is common to doctor's who are commonly charged with managing ACT. Even the clinics are set up to operate under the same misapprehension. What is not understood is that INR (more precisely, the time to form thrombin, expressed as INR for the sake of easy universal comparison) is highly variable over the course of days and weeks. Worse, they don't seem to understand that it can and will change dramatically, and for the long term, in the space of days, if not hours, and without warning.
When the researchers in Hamilton did the study, they actually DID monitor all of the patients on the regular four week schedule, as normal. There were extreme results in the group who were suppose to represent the 12 week interval (and for whom 'sham' results were being reported).
"A physician at the CMC reviewed all true INR results
in the 12-week group for extreme values, defined as less
than 1.5 or 4.5 or greater. When INR results that were to
have been reported as sham values were extreme, the true
result was forwarded to the treating physician, as were any
follow-up measures (usually 1 week after an extreme INR
was found). True INR results were also always reported for
measures in association with a clinical event or perioperative management. A manual record of true INRs in both
groups was kept at the CMC."
This short paragraph tells you everything you need to know about the value of the study. There were patients who were deemed to have dangerous results in the interim tests, which they would not have been having if they we part of a 12 week regime. Those results were reported to the managers who could then act appropriately to prevent harm.
How many patients would it be ok to harm or lose in order to save a few dollars on test strips?
One other statistic worth looking at is that there were both fewer extreme INRs reported and fewer dose changes for the longer interval group. The study doesn't adress whether that is random, in spite of the interval differences, or because of the interval difference. In other words, were there fewer dose changes because of the longer interval, and was that beneficial, harmful or inconsequential to the patients.
I'm comfortable with my 1-2 week intervals right now, and won't be changing them any time soon. For fewer than 20 dollars per month (about what I spend in Starbucks each month). I can buy piece of mind, and possibly prevent a stroke or bleed.
