Question about INR changes when you skip a dose and get tested in different places

[T in YVR]

Hi,
Not sure if you saw my thread under "Post Surgery" ("Blacked out, hit my head and concussed...can't wait to get off Metoprolol/Coversyl"), but I had a head injury and was in and out of the hospital a couple times this week with my share of issues. Anyways, the doctors had me stop my warfarin for 1 day in order to lower my INR and help stop some internal bleeding in my sinus cavity. When I was tested at the hospital yesterday morning, my INR was 3.2. Its normally been in the low 2's. I was also taking Tylenol the last few days, so that may have contributed to the jump to 3.2. I then skipped my warfarin dose last night as requested by the doctors. I got tested today, and my INR (at a lab) was 2.1 - roughly 24 hours later. I had 2 questions, I was hoping someone could shed some background and experience on:

1. If you skip a dose of warfarin (whether intentionally or not), is it likely that your INR could drop from a higher # like 3.2 down to 2.1 in 24 hours? I had also stopped the Tylenol - maybe that also contributed to the fast drop. I was just a bit surprised at how fast it fell.

2. Is it possible to get significantly different readings between a lab (which has to courier it across town to get the test done after the blood is collected) and a hospital (which tests your INR in-house within minutes of it being withdrawn)?

Thanks,
Tony

 

[dick0236]

1. If you skip a dose of warfarin (whether intentionally or not), is it likely that your INR could drop from a higher # like 3.2 down to 2.1 in 24 hours? I had also stopped the Tylenol - maybe that also contributed to the fast drop. I was just a bit surprised at how fast it fell.

2. Is it possible to get significantly different readings between a lab (which has to courier it across town to get the test done after the blood is collected) and a hospital (which tests your INR in-house within minutes of it being withdrawn)?

Thanks,
Tony

A drop of that much in a 24 hour period would be a little unusual for me.....although I wouldn't worry about it since you stayed within your range(I assume 2-3). For me, a one dose hold(5mg) would lower my INR +/- .8 after a COUPLE of days. It could also have been the difference in testing methods of the hospital and the lab. I do not believe that Tylenol has an effect on INR. I added 1000mg Tylenol daily for back pain several years ago with no discernible impact on INR.

 

[newmitral]

Hi,

1. If you skip a dose of warfarin (whether intentionally or not), is it likely that your INR could drop from a higher # like 3.2 down to 2.1 in 24 hours? I had also stopped the Tylenol - maybe that also contributed to the fast drop. I was just a bit surprised at how fast it fell.

2. Is it possible to get significantly different readings between a lab (which has to courier it across town to get the test done after the blood is collected) and a hospital (which tests your INR in-house within minutes of it being withdrawn)?

Thanks,
Tony

Hi Tony,

1.
For me, a drop of that magnitude would be expected. I don't have tests separated by exactly 24 hours, but I have one case where I dropped from 4.1 to 3.0 in two days by skipping one dose the first day and taking half a dose the second day.
I have another instance where I dropped from 3.0 to 1.5 in 2 days, also by skipping only 1 dose the first day and taking 1/2 dose the second. This was in preparation for some minor surgery, so the lower-than-target-range INR was planned.

----------

2.
The two readings should not vary by much more than a few tenths if the labs are doing their job properly, but of course, anything is possible if one or both labs are inaccurate.

----------

I take a large daily dose of warfarin (12.5mg/day) and I have an unsubstantiated theory that those needing a larger dose of warfarin seem to drop more quickly when a dose is missed. I don't know your warfarin dose, but if it is high, that would be in line with this anecdotal opinion of mine.

 

[Freddie]

Everyone is different when ones skips/holds a dosage, if it were me I'd probably get the same result as you did Tony.

It is very possible to get different readings from the lab and hospital......but it really shouldn't be no more than a .4 difference. The Canadian standard for INR lab testing has a variance of <.2> plus another .1 for human judgement. Also the tests are to be done in 3 hours then relayed to the doctor within 4 hours. And yes, getting it done in the hospital results would happen much faster. (rather nice to have a lab tech as a neighbour )

What is your INR range?

 

[Gail in Ca]

I rarely skip a dose anymore as it always caused my inr to drop a lot. I will lower a dose but not skip it. I was told that tylenol will change the inr if you take more than 1500 mg a day. Most doctors think it doesn't affect inr. The readings are probably within a small range of each other like 0.2 maybe. Now that you know your inr drops fast, you can tell the coumadin person that and hopefully not have to skip a dose anymore.

 

[T in YVR]

Thanks everyone.

NewMitral - I have been taking 8.25 - 8.50 mg daily. I am 4 months post op so still adjusting it a bit. My dosage amount has been slowly increasing but since the operation, but it seems to be about right for now.
Freddie - I have a target range of 2-3.
Gail - My Tylenol was about 1,000mg daily for 3 days. I had to skip a dose of warfarin at my doctors orders due to internal bleeding that would not easily stop. It has since stopped and I am now (as of tonight) back to my 8.5mg dosage, and get tested again on Tuesday.

Thanks again,
Tony

 

[pellicle]

Hi

Anyways, the doctors had me stop my warfarin for 1 day in order to lower my INR and help stop some internal bleeding in my sinus cavity. When I was tested at the hospital yesterday morning, my INR was 3.2. Its normally been in the low 2's. I was also taking Tylenol the last few days, so that may have contributed to the jump to 3.2. I then skipped my warfarin dose last night as requested by the doctors. I got tested today, and my INR (at a lab) was 2.1 - roughly 24 hours later. I had 2 questions, I was hoping someone could shed some background and experience on:

1. If you skip a dose of warfarin (whether intentionally or not), is it likely that your INR could drop from a higher # like 3.2 down to 2.1 in 24 hours? I had also stopped the Tylenol - maybe that also contributed to the fast drop. I was just a bit surprised at how fast it fell.

yes. However what remains in question is "was it actually 3.2" and "did it go to actually 2.1"

Assuming margins of error it could have for instance dropped from 2.9 to 2.5

as to drops, perhaps you may find this post interesting.

http://www.valvereplacement.org/forums/showthread.php?41411-Oops-missed-dose&p=535366#post535366

I've also tested my model and found that my INR conforms well to what it suggests. Both lines (predicted and trend) are in there because my measured INR seems to fall between them.

Also as INR does naturally go up and down (see below)

if your timing of dropping a does coincided with a natural down cycle then that would amplify it.

2. Is it possible to get significantly different readings between a lab (which has to courier it across town to get the test done after the blood is collected) and a hospital (which tests your INR in-house within minutes of it being withdrawn)?

definitely, this is well discussed both here and in the medical journal literature. It is accepted that there are multiple "standards" for reagent preparation and that there will be variances (as much as 0.3) between labs who follow tight standards, and much more for those who follow looser standards adherence in preparation and storage of blood samples.

perhaps its a little wordy but this post may be helpful to understand the sorts of relationships between body metabolism cycles and INR that can occur

http://www.valvereplacement.org/for...from-Warfarin-to-Coumadin&p=548774#post548774

 

[Cooker]

when I miss a dose I don't give it a second thought ... just pick up the next day as usual ... not really a big deal ... if one missed dose would cause problems I'm sure another avenue would have been taken ... we are human and their for we miss a dose from time to time....:thumbup: