I have some major concerns about the advice that I receive from my pathology lab when they indicate that changes to my INR are required.
My INR target range is 2.0 to 3.0. Now if you have read the 2 posts below, you will realise that the measurement of INR is not particularly precise, and that adds to the difficulty of assessing just what changes are required.
A few weeks ago, I was on a schedule of 4.5 mg and 5 my alternative days. On testing, my INR was below 2.0, at about 1.7.The pathology lab advised that I should now take 5 mg warfarin on Sunday, Tuesday Thursday and Saturday, and 4.5 mg on the remaining three days each week.
Now on my original schedule I would get 7 days of 5 mg and 7 days of 4.5 mg each fortnight, making a total of 66.5 mg per fortnight, or a total of 33.25 mg/week.
On my pathology labs new schedule, I would get 4 days of 5 mg per week, and 3 days of 4.5 mg/week, or a total of 33.50 mg/week.
So, although my INR was significantly below 2.0, at 1.7, the dosage suggested increased my warfarin intake by only 0.25 mg/week, or about 0.75% !!!!
My INR of course did not shift.
Again, quite recently, my INR was 2.0, and the lab called to change my dose.
I had been on 4 mg and 4.5 mg alternate days, a total of 59.5 mg/fortnight, or 29.75 mg/week.
Their new schedule they suggested was 4 mg on Sunday, Tuesday, Thursday and Saturday, and 4.5 mg on the remaining three days each week. This resulted in a dosage of 29.5 mg/week.
So the dosage suggested was in fact a decrease of 0.25 mg/week or about 0.75%, in spite of the fact that my INR was at the lower level recommended!!!
I rang to point this out, and they changed my dose, somewhat reluctantly, to 4.5 mg Monday to Friday and 4 mg on Saturday and Sunday. This results in a total dosage of 30.5 mg/week.
So their new recommendation was an increase of 1.0 mg/week. or 3% increase, compared to their first recommendation of a decrease of 0.25 mg/week or a decrease of 0.75%.
Clearly, I have no confidence in the information or recommendations provided by my pathology lab.
Now let's have a look at what is really required for changes in INR dosage to have a real effect. Below is part of an abstract from an article published in 2000.
- ALWAYS ask for your INR when you get tested, don't just blindly accept the dosage changes recommended.
- Keep records of your INR and dosage and dates tested
- If changes are recommended, do the arithmetic yourself, and see just how much of a change in your weekly dose has been proposed - if it is less than 5%, ask why!
|>10.0||Stop warfarin. Contact patient for examination.|
|7.0-10.0||Stop warfarin for 2 days; decrease weekly dosage by 25% or by 1 mg/d for next week (7 mg total); repeat PT³ in 1 week.|
|4.5-7.0||Decrease weekly dosage by 15% or by 1 mg/d for 5 days of next week (5 mg total); repeat PT in 1 week.|
|3.0-4.5||Decrease weekly dosage by 10% or by 1 mg/d for 3 days of next week (3 mg total); repeat PT in 1 week.|
|1.5-2.0||Increase weekly dosage by 10% or by 1 mg/d for 3 days of next week (3 mg total); repeat PT in 1 week.|
|<1 .50=".50" td="td">1>||Increase weekly dose by 15% or by 1 mg/d for 5 days of next week (5 mg total); repeat PT in 1 week.|
I'd suggest that ytou use these as an indication of what should be suggested by your pathology lab