A bit of warning to anyone thinking about using a Coaguchek XS to monitor INR. If you have tested positive for lupus antibodies the machine tends to give false high INR results compared to venous blood tests.
Check out the small print in the information that comes with the test strips (there is no information on this with the machine unless the company have changed that since I bought my own machine a year or so ago). This is what the information says:
"Antiphospholipid antibodies (APA) such as Lupus antibodies (LA) may falsely prolong coagulation times, i.e. they may cause false-high INR values and false-low Quick values. Where APA are known to be present, it is imperative that a result be obtained using an APA-insensitive laboratory method for comparison."
I am positive for Lupus Antibodies and my GP and I have found that my Coaguchek over reads my INR by about 20% but can be more as it is not a constant error as it depends on antibody levels. Now that isn't too much of a problem when my INR is 4.5 on the machine as it still means that my blood is probably around 3.5 BUT it is a problem if my INR drops into the 2s and I think that is one of the reasons I became ill last month as my machine was reading 2.4 but if that was false-high then I was sub-therapeutic but I wasn't injecting as at the time I was instructed to only start that if my INR went below 2.
I went to my GP and showed him the test strip information and we discussed it and agreed that I now start injecting Dalteparin if my INR on my machine drops below 3 (it was 2) and once a month I am doing a venous and home machine test on the same morning to compare the results. My GP has checked with the haematology department at the hospital lab where the bloods are sent and has confirmed that they use an APA-insensitive lab method.
If you are self-testing and have Lupus antibodies take the information sheet along to your Dr and make sure that a) they know about this and b) they factor it into your INR management.
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travelnut
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Thanks Travelnut, this is really useful information. I did my very first self test today with my coaguchek xs machine and got the result of 2.6 (my range is 2.0-3.0). So if it has over-read by 20% then potentially he real reading was around 2.3 (if my maths is correct!) which would still have me within my range. So I guess that going forward, I just need to be sure to ensure my INR is between 2.5 and 3.0 to always be in the real range according to the coaguchek machine.
The thing is Stuart that you may not be getting false-highs. That is why they have suggested to me comparing against a venous sample fairly often. If it was a constant error it would make life a lot easier!
Also under finger prick testing clinic and will definately be asking for a venous comparison regularly. This i`ve just discovered is recommended for patients with APS, Lupus antibodies. Having been on warfarin this time for 18 months and never had a venous sample done, i`m concerned, cos how I feel doesn`t always tie up with INR.
Thank you so much for posting this.
Take care gentle hugs Jessielou xxxxx (Sheena) xxxx
Ps just been doing some research on this and is a bit scary!!!
Hi Jesselou I would definitely ask for some comparisons. If nothing else that is good practice from a quality assurance point of view. Having said that I didn't have any venous samples for around 18 months and the discrepancy between my machine readings and the lab ones was only picked up when I was ill and the doctors suspected another clot - which is too late! That's one of the reasons why I wanted to make everyone here aware of this potential problem (I say potential as it may not be all or even most people).
This is really interesting! But my worry is how do I monitor when I am sero-negeative? I dont know about my Lupus Antibodies therefore how will I know if I should calculate for the 20% or not?
Another question (sorry), travelnut you indicate that you have heparin on the side just in case. Is that something we should have in the house? I am on heparin but am only given enough for the time I am prescribed because of the cost of them. I am supposed to be calling Prof next week to see how things are and then decide if I come off and switch over to warfarin. Should I ask to have spare inj around just in case?
I am not sure if there will be a discrepancy or not if you are sero-negative. The only way you would know is to run a series of finger prick tests at the same time as venous tests and see how similar the results are. I've been told that there will always be some differences but it is usually 5% or less (which for my INR target means 0.1 or 0.2 difference between the finger prick and venous tests at the most). If you several comparison tests then your Doctor should be able to get an idea if the differences are higher or not and then they can advise you accordingly.
Yes, I always have a 5 day supply of Dalteparin at home and when I travel (which I do a lot). This is down to several reasons. First, I have clotted when my INR has been between 2 and 3 so the doctors know that I have events when I am on warfarin. Second, I self manage as well as self test so I control my warfarin dose and also decide when to take the injections based on the guidelines I have agreed with my doctor (these are the ones we have recently changed based on the reading discrepancies). Third, I have a very supportive and understanding GP who has really put himself out to help me so that having APS has the least impact on my life as possible whilst keeping me as safe as possible from recurrent clotting events. Last, I do a lot of travel so with changes in diet and things my INR does become even more unstable than usual so I take the Dalteparin in case my INR drops when I am overseas so that it is normal/slightly high when I fly back to the UK.
There isn't too much research on this at all from what I can see but there was a paper published in the late 1990's that highlighted this problem. If anyone is interested this is the link but this is quite an old study now - annals.org/content/127/3/17...
This is interesting info. I have a venus test at GP every 2 months (for first 18 months self testinh) and at that time I also did a coagucheck test with nurse. Results have always been comparable so I am happy to continue self testing. (I now have a proffesional coagucheck test with nurse every 4 months and call my own self test results in weekly)
My INR range 4 to 5 when I am under 3.4 I know. I have definatley noticed that I know when my INR is low (symptoms poor balance, naviagtion, cognative, speech, fatigue etc) and when I prick my finger its hard to get a drop of blood out! (I will buy larger size yellow lancets next time this lot are to small white ones)
I wonder if you and other members "just know" when INR is to low?
It sounds as if your GP set you up well in the first place Garry when you switched to self testing and it is good news that it doesn't seem that your INR is affected.
Personally, I haven't got the 'knack' of knowing when my INR is too low as yet. I have an inkling that it may be a bit high or low with certain symptoms but it doesn't always match the INR result! I suppose keeping a diary of how I feel and symptoms may help to pin down the INR level at which I get symptomatic but to be honest I don't really want to dwell too much on having symptoms.
Hello All...The INR home monitoring should not be trusted when you have APS...The strips interact with the antibodies from our APS and you will never get an accurate read... I almost was set up through my GP's office with the ALERE machine, however they were smart and wanted a Lupus disclaimer letter signed first...( they know that it provides unreliable inr reads. Then what is the sense of using these machines. If it states I am 3.5 which is theraputic, I could actually be 1.9.....I would rather go for a stat lab draw than the chance of throwing a clot and having a stroke.....
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