Oops - missed dose

[pem]

Hi. Long time since I've been on. Hope everyone is doing well and that newcomers are getting the great support I got when I first signed on.

It turns out that when I home tested on the 15th (Friday - 3 days ago), my INR was 2.2. I had been taking 8.5mg/day. So I bumped it up to 9mg/day beginning Friday night. I took 9mg Friday, 9mg Saturday, and the FORGOT on Sunday. I just realized this tonight when I went to take my medicine. So I measured my INR. It is 1.7. This makes me a bit nervous, especially since I was already low out of range on Friday and have been trying to boost it up. So tonight (about an hour ago), I took my usual 9mg and then decided to take an extra 5mg (doubling up is contra-indicated, so I took 1.5 times the usual), and then I'll plan to make up the rest tomorrow and the next day. Does that make sense?

Also, given that my INR is so low (1.7) should I consult my doctor tonight about bridging with heparin (which I have at home)?

Appreciate any suggestions on this.

Thanks,
pem

 

[pellicle]

Hi

It turns out that when I home tested on the 15th (Friday - 3 days ago), my INR was 2.2. I had been taking 8.5mg/day. So I bumped it up to 9mg/day beginning Friday night.

as I understand it there is some lag in the INR responce due to the fact that warfarin actually builds up in the system (it has a half life of about 2 days, so successive days adds to what is there).

I took 9mg Friday, 9mg Saturday, and the FORGOT on Sunday.

happens to me from time to time, less now that I use an alarm on my phone for my dosage time reminder. There are a few strategies on this, some say to take half that dose within 12 hours others suggest not worrying about it, there are some other views.

I just realized this tonight when I went to take my medicine. So I measured my INR. It is 1.7. This makes me a bit nervous, especially since I was already low out of range on Friday and have been trying to boost it up.

what is your target range? Anyway as I understand it the relationship between INR and thrombosis is complex. I understood that there were more risks from rapid changes, than slow low dips or rises. Personally I would not panic, but just resume dose that you have been taking. Perhaps add half the missing amount.

So tonight (about an hour ago), I took my usual 9mg and then decided to take an extra 5mg (doubling up is contra-indicated, so I took 1.5 times the usual), and then I'll plan to make up the rest tomorrow and the next day. Does that make sense?

seems to

Also, given that my INR is so low (1.7) should I consult my doctor tonight about bridging with heparin (which I have at home)?

If your GP is quite experienced in managing INR and has a lot of training in the area then perhaps yes, personally I'd not be fussed but that is me. My surgeon wasn't worried about my INR (and I have a mechanical aortic) when last in hospital and my INR was dropped to 1.7 for a debridement surgery. I was not put on heparin on that occasion.

Below is the graph of the section of the data that I keep on my INR and dose:

where there is no warfarin dose line that is where the dose was withheld pre surgery. You can also see a drop in dose to 4mg where a stand in surgeon dropped my dose (not without a discussion mind you) to 4 because he was worried I'd overshoot....

the X scale represents days from admission, there are two Y axes. Also, the days without INR are days where none was taken (like in ICU). Most measurements were veinus samples and the latter ones were cross referenced against my coaguchek with very close matches.

HTH

 

[pem]

Hi pellicle,

Thanks much for your reply. It's comforting.

I think the only reason I'm nervous about this one is that my INR hasn't been this low since my valve replacement. By the way, I have an ATS (now Medtronic open-pivot), which I think is the same as yours.

I just spoke with the on-call cardiologist. He advised me to recheck in 24 hours and if I'm still a bit low, take 10mg. He said lovenox (which is what I actually have at home - not heparin) would not do the trick and to make a difference I'd need to check into the hospital and get IV heparin. He did not think this situation warranted such action. Which I would expect, but it is nice to hear your doctor say it.

By the way, since you are quantitative and keep tabs on your INR, I am interested to know if you have any parallel (coaguchek vs lab) readings you could share? I'd be happy to share mine back. I think there might be person-to-person differences in how the machines respond to different blood chemistry and have a predictive model that helps to calibrate readings to the home monitors - if you are interested. Of course, the model needs to be fit to your own parallel checks first to work predictively.

Thanks again,
pem

 

[pellicle]

Hi

Thanks much for your reply.

glad I could offer something useful

By the way, I have an ATS (now Medtronic open-pivot), which I think is the same as yours.

interesting ... I didn't know that till just now.

By the way, since you are quantitative and keep tabs on your INR, I am interested to know if you have any parallel (coaguchek vs lab) readings you could share?

sure, well such as they are (meaning not suitable for "publication")

I first tried using the coagucheck XS in the first month after surgery. I didn't get good results, got fed up easily and didn't get good bleeds. So I left it on the shelf for a year and then came back to it.

These results are over a weekly stab and jab comparison when I felt that I'd got my technique better. (meaning that each sample is separated by about a week)

I had a discussion about results and issues here (look up this thread http://www.valvereplacement.org/forums/showthread.php?41136-the-15-second-rule there was for me some good information from both this thread and my discussions with Roche here in Australia at about that time). From about that time I got much more consistent results. I also learned more about the issues relating to peripheral blood flow (subcutaneous) and the cascade of reactions there that make 'milking' the finger after a stab a "bad thing to do" when using a meter such as the Coaguchek XS.

Having had problems with getting blood in the first 15 seconds and not wanting to really slice myself, milking seemed inevitable and in the early days I blew strips from the 'error 5' of not enough blood for a sample.

These later results are better and more consistent with lab results.

and have a predictive model that helps to calibrate readings to the home monitors - if you are interested.

interesting ... what is that?

 

[dick0236]

I just spoke with the on-call cardiologist. He advised me to recheck in 24 hours and if I'm still a bit low, take 10mg. He said lovenox (which is what I actually have at home - not heparin) would not do the trick and to make a difference I'd need to check into the hospital and get IV heparin. He did not think this situation warranted such action. Which I would expect, but it is nice to hear your doctor say it.
pem

This is good advice. We all miss a dose every now and then. Bring it back with minor dosing changes.

 

[Protimenow]

This is an interesting discussion. I've mentioned that one of our members had a predictive algorithm for adjusting InRatio results to lab results. I have never tested with a CoaguChek XS, but it's interesting to see a good relationship between its results and those of a lab.

According to a paper that I downloaded a year or so ago, having an INR below range is not a major problem if you're more than 3 months post-op, and don't KEEP it that low. If I recall, their approach was a one time dose of 1.5 times your standard dose. (It looks like you did almost exactly that). Where you apparently can run into trouble is if your INR is below 2 for a week or more. (Last year, mine WAS - I trusted my meter, and didn't pay enough attention, and had a stroke). Now, more than ever, I'm concerned with weekly testing and getting ACCURATE results. I've been having a monthly blood draw, and also comparing the results to my InRatio (and also, often, to my Protime 3 meter). I haven't gotten obsessive about testing, but I want to feel comfortable that I'm in range.

A few other things: I've been keeping a spreadsheet with my INRs -- date, time, prothrombin time, INR, machine used, weekly dose, and comments about any factors that may be important. This 'INR Diary' is a useful history, and also can be useful for convincing doctors who may be reluctant about these mere mortals who think that they're capable of taking their own INRS actually getting Warfarin refils.

I just got a Coag-Sense meter. It's an interesting machine. It times the ACTUAL time that it takes for blood to clot (rather than looking at eletctrical impedance or other secondary factors). There's a small wheel in the strip - when the blood is dropped on the strip, the blood mixes with reagent, the wheel spins, and an optical sensor detects when the clot has formed. This also wants blood in the first fifteen seconds.

There's a bit of a learning curve related to getting that first drop, moving it into a collection tube or micropipette, then dropping it onto the strip. I've learned a couple things about getting a good drop that I didn't really think about before (and these can apply to the InRatio and CoaguChek XS, too: Do the basic finger prep -- warm the finger (usually by rinsing in warm water), pinch the finger below the knuckle to get the blood to pool in the fingertip, and (here's where there's the interesting difference) after incising the finger, squeeze the edges of the incision to open the hole slightly. This actually DOES seem to help get a bit more blood out, and it's something that I didn't think of doing.

Another thing that I learned - after years of using 21 gauge lancets in a lancing device set on maximum depth -- some of the one time use lancets (I've had good luck with Unistik Heavy lancing devices) actually seem to go a bit deeper than my other devices, so you can get a better drop of blood.

In the past, I've almost always gotten enough blood for the InRatio using my old setup (and the InRatio needs more than the Coag-Sense), but I'm planning to switch over the Unistik 3 Heavy to (probably) assure that I get a large enough drop. If you've had to 'milk' your finger, you might consider trying one of the 'one use' lancing devices that are designed to get an adequate drop for INR testing. (No - I don't work for these companies)

 

[pellicle]

Hi

If you've had to 'milk' your finger, you might consider trying one of the 'one use' lancing devices that are designed to get an adequate drop for INR testing. (No - I don't work for these companies)

as the only person so far to mention inadequate blood sample was me, I'll assume you are directing this to me.

Yes, that *was* a problem for me in 2012, but I've got it sorted now.

thanks

 

[pem]

Update: I took 14mg coumadin last night and checked again tonight. Still 1.7! Thinking I should get a lab check tomorrow.

The doctor on call said to take 14mg coumadin again tonight since I tolerated it last night (not sure what that means). I mentioned that I have lovenox on hand, so he had me initiate lovenox tonight and to continue with it twice daily until my INR climbs back up to at least 2.5.

Is the lovenox additive with the coumadin? Do I risk over-anticoagulating?

Does this seem too drastic of a dosing change?

Thanks,
pem

 

[pem]

Thanks, Dick. Does my current course of action seem reasonable to you?
Best,
pem

 

[pem]

Hi



glad I could offer something useful


interesting ... I didn't know that till just now.



sure, well such as they are (meaning not suitable for "publication")

I first tried using the coagucheck XS in the first month after surgery. I didn't get good results, got fed up easily and didn't get good bleeds. So I left it on the shelf for a year and then came back to it.

These results are over a weekly stab and jab comparison when I felt that I'd got my technique better. (meaning that each sample is separated by about a week)

I had a discussion about results and issues here (look up this thread http://www.valvereplacement.org/forums/showthread.php?41136-the-15-second-rule there was for me some good information from both this thread and my discussions with Roche here in Australia at about that time). From about that time I got much more consistent results. I also learned more about the issues relating to peripheral blood flow (subcutaneous) and the cascade of reactions there that make 'milking' the finger after a stab a "bad thing to do" when using a meter such as the Coaguchek XS.

Having had problems with getting blood in the first 15 seconds and not wanting to really slice myself, milking seemed inevitable and in the early days I blew strips from the 'error 5' of not enough blood for a sample.

These later results are better and more consistent with lab results.



interesting ... what is that?

It looks like the coaguchek slightly underpredicts for you, but the readings are close enough that you would probably not benefit from any adjustment.

By the way, did you find that milking artificially inflated or reduced your INR?

Thanks,
pem

 

[dick0236]

Thanks, Dick. Does my current course of action seem reasonable to you?
Best,
pem

I think you are retesting too soon after the changes. The extra 5mg you took last nite(monday?) will have little effect on Tuesday(too soon)......however, the missed dose on Sunday will show up on a Tuesday test. Wait two or three days between testing to allow the warfarin to enter your system. I am not sure how the lovenox will affect your INR, if at all, during this time as I have never had to use lovenox. I would not worry and my guess is that you will be in your range, or close, by Friday.

 

[pem]

Thanks, Dick. You are the voice of experience and I greatly value and trust that.

They advised me to retest tomorrow afternoon and then call the cardio office. But I will consider my findings in the context of what you said and try to remind them about the delayed effect. I am always cognizant that the cure can be worse than the disease if one isn't judicious. Fortunately, my own cardiologist is a real pragmatist and very bright, so I am hoping to talk with her.

Best,
pem

 

[Protimenow]

As I noted earlier, as long as your INR isn't below 2.0 for more than a week (or perhaps a few days), you should be okay. Catching it early, as you did, and increasing your dose right away seems like the right thing to do. You probably didn't need the Lovenox - but it shouldn't hurt. Yes, it takes time for the full effect of warfarin to show up on tests. Yesterday's dose won't appear on today's INR. I would not be surprised if your INR isn't higher tomorrow and even higher on Thursday. I suspect that getting back into your daily dosing protocol, now that you've increased your dose, should be all that you need to stay in range. Again--being below 2.0 for just a couple days should NOT be a problem--according to recent articles.

 

[pellicle]

It looks like the coaguchek slightly underpredicts for you, but the readings are close enough that you would probably not benefit from any adjustment.

it could easily be that one has different rounding to the other too. So yes, I'm not worried about the differences either

By the way, did you find that milking artificially inflated or reduced your INR?

I was initially not milking, but wanting longer than the 15 sec to get the required blood, this gave me a higher INR than the lab by a margin of about 0.3 ... I think that the milking (don't have that data on my dropbox and I'm at work atm) was reading lower. But that's unreliable as I was also taking longer to get that sample than 15 sec.

I have since gone with getting the sample out in the 15 sec. I use a firm but not dreadfully tight wrapping of cotton at the hand end of the second knuckle for some 30 sec before lancing. When I use the lower lance depth it starts to produce just a pinprick of blood, then I bend the finger and a really good sample gets squeezed out in moments.

This way I get my sample with no massaging and within 5 seconds of lancing.

 

[pellicle]

Oh, and PEM, this model (used in a spreadsheet) will give you an approximation of what will be happening to the warfarin in your system.

Make C2 your warfarin dose, fill this down for the series of C

In Colum D
start with this series and continue
=C2
=D2+0.75*C2
=C4+(0.75*C3)+(0.5*C2)
=C5+(0.75*C4)+(0.5*C3)+(0.3*C2)
=C6+(0.75*C5)+(0.5*C4)+(0.3*C3)+(0.25*C2)
after here you can fill down

NOTE: this model does not take into account actual metabolism NOR the actual bioavailability of the dose (which varies from person to person depending on their metabolism).

However it does provide a simple working model for you to undertake a little what if analysis on "what if I miss a dose". Especially when you factor in the rate of drop of INR observed in my above chart to estimate the biological response to a missing dose you can get a feel for the reaction of the system (your bodys system) to the changes.

This is of course a SIMPLE model, however my experience in modelling suggests that more complex models while potentially producing more accurate results can vary more wildly when the input parameters are in error. Essentially the less parameters the lower the accuracy but the lower the tendency for wildy inaccurate results too.

 

[pellicle]

Hi Dick

....however, the missed dose on Sunday will show up on a Tuesday test. Wait two or three days between testing to allow the warfarin to enter your system.

this is conventional wisdom, however I wonder about it, as my results from my recent hospital stay (graph above) seem to show a much more noticable reaction, one day seems to have been visible. Of course the measurement taken was the duration you suggest, but the reaction to resumption was clearly faster (and I was being tested daily (and yes by IV sample)).

more data is needed (by me at least).

 

[pellicle]

Hi

having a bit of time on my hands after dinner this evening I thought (as I had "some" data) I'd throw together the data I had from my hospital stay into a spreadsheet alongside the simple mathematical model I have discussed. I applied a constant scaling factor (7.5) to bring the calculations to be close to that of the INR that I had to start with. I think the results are interesting

of course the mathematical model doesn't provide any buffering (as the body would), and so drops instantly that inputs are dropped, as well as raises tightly with no dampening (buffering) as soon as the inputs are raised. I find that the inter-reactions of the set are interesting.

I wish I had more INR data, but as my last reading was in the morning of going into hospital (and I didn't take my coaguchek) I just don't have it. I'd like to know how fast it drops! Also I wish I had opportunity to have INR measured on the day of surgery and in ICU.

Perhaps next time ;-)

PS: I don't expect that my INR went below 1.5 ... but then that'd be guessing

 

[Protimenow]

Interesting findings, Pellicle.
One of the problems that I have with comparing meter results to lab results is that lab results aren't always very good. The quality of the lab results is also a product of how the sample is handled after the blood is drawn, and how accurate the value of the reagents is. I have my blood drawn at a hospital, and I trust the hospital lab. A few months ago - on the same day as the hospital blood draw - a clinic took my blood. The Hospital lab result put me right in range. The clinic's result was slightly below range. (Sorry, I'm being lazy and didn't look at my spreadsheet). The difference between the two labs was almost 1.0. The doctor at the clinic - apparently knowing nothing about anticoagulation management - prescribed a one time doubling up on my dose. This was crummy advice - but certainly fit the 'increase the weekly dose by 5%' model -- it would have made my INR spike a few days later, but drop me right back where I was in a week.

The point here -- you probably won't get the same result from different labs. I trust a hospital lab. I have less trust of a clinic or doctor office, where the blood may be mishandled, or improperly stored, and the actual lab may not be as careful about doing the test as a hospital lab would be.

 

[pem]

As I noted earlier, as long as your INR isn't below 2.0 for more than a week (or perhaps a few days), you should be okay. Catching it early, as you did, and increasing your dose right away seems like the right thing to do. You probably didn't need the Lovenox - but it shouldn't hurt. Yes, it takes time for the full effect of warfarin to show up on tests. Yesterday's dose won't appear on today's INR. I would not be surprised if your INR isn't higher tomorrow and even higher on Thursday. I suspect that getting back into your daily dosing protocol, now that you've increased your dose, should be all that you need to stay in range. Again--being below 2.0 for just a couple days should NOT be a problem--according to recent articles.

Thanks, protimenow. I think recalling your own experience with discovering a low INR in that range (was yours 1.4 or 1.7?) when you were in the hospital caused me concern about this. I appreciate your feedback. Could you send me a link to that recent article?

It turns out my INR is back up to 2.2 as of tonight. I have been advised to take 10mg tonight (instead of my usual 9) and continue lovenox until I am in the therapeutic zone. I believe an INR of 2.2 is probably fine for this valve, but I am following doctors orders.

Best,
pem

 

[pem]

it could easily be that one has different rounding to the other too. So yes, I'm not worried about the differences either



I was initially not milking, but wanting longer than the 15 sec to get the required blood, this gave me a higher INR than the lab by a margin of about 0.3 ... I think that the milking (don't have that data on my dropbox and I'm at work atm) was reading lower. But that's unreliable as I was also taking longer to get that sample than 15 sec.

I have since gone with getting the sample out in the 15 sec. I use a firm but not dreadfully tight wrapping of cotton at the hand end of the second knuckle for some 30 sec before lancing. When I use the lower lance depth it starts to produce just a pinprick of blood, then I bend the finger and a really good sample gets squeezed out in moments.

This way I get my sample with no massaging and within 5 seconds of lancing.

I'll have to give that technique a try - thanks!
pem