Huge discrepancy between the lab and CoaguChek XS

[sharky7]

some points on error margins.
1) error increases as INR does, which means a graph like this is possible
View attachment 889094
if you're unfamiliar with reading graphs let me add in one or two with guides

View attachment 889095

so in general (in that study) outliers tend to be off higher (red line was Lab = 3.6 while XS gave 4.6

Now, if you were (say) INR Target = 2.5 then either of those high figures would be reason to turn your INR around. However the XS would steer you back to the middle (the target) a little earlier.
Around INR = 2 the differences were less, which is good because 2 and lower is increasingly not where you want to be.
Around INR = 2.5 theyr were quite close

Also important to keep in mind "Clinical Significance" ... is there really any importance between being 2.3 or 2.7? Remember also that all of this is fuzzy. We have a range of INR's where its pretty safe and the aim isn't to get a number its to not have an event.

By being as close to our target as we can we minimise the risks of harm

HTH

YES, and agreed 100%, and I would add to that, I think that it is not being brought here enough and for all here to comment about perhaps,
and the aim isn't to get a number its to not have an event. ["and the aim isn't to get a number its to not have an event.
By being as close to our target as we can we minimize the risks of harm"]

Thank you!

 

[ATHENS1964]

Our health service did all that years ago, with hundreds of thousands of tests, and concluded the machines are similar quality results to labs. No need to keep doing the lab tests now. Good enough for me.

Because it's just a device and devices often break down or malfunction and because we don't have any liquids to check the device at home for its accuracy. It is good to test it once a year, either by doing tests in a lab or with another device. Also, laboratories check their devices regularly, there is a relevant protocol.

 

[LondonAndy]

Because it's just a device and devices often break down or malfunction and because we don't have any liquids to check the device at home for its accuracy. It is good to test it once a year, either by doing tests in a lab or with another device. Also, laboratories check their devices regularly, there is a relevant protocol.

Totally agree. Mine is checked every six months against the clinic's machine, as I reported earlier.

 

[carolinemc]

First of all hello, this forum and its members were incredibly helpful while learning about valve surgeries

I'm a 28 year old male, almost 4 weeks out of my mitral valve replacement, and I've had quite a lot of trouble setting my INR right in this period. We started with a low dose of anticoagulant medicine (Sintrom), and the doctors kept on increasing my dose slightly. I also got a Coaguchek XS in order to compare my lab values.

The thing is, even though my INR values were low they were steadily increasing. My initial values were 1.6 (and Coaguchek reported 1.8) on 30/01, then it started growing towards 1.8 (Coaguchek 1.9) 03/02, and then today/this morning my lab value was 1.56, while Coaguchek displayed 2.2...

I'm unsure what to think of this. I tested this morning with Coaguchek, and I was confident that my lab value will be relatively close to the CoaguChek value but it is quite far apart... (also keep in mind that I further increased my dose since the last chek 5 days ago). My diet is relatively stable, my exercise is also stable (40 min walks 2x a day), my sleep too. I have no explanation how this is possible.

One thing that I think could be possible is that the lab messed up due to some reason (simple mistake or even incopetence). I'm from a small european country, and I moved back to my hometown (10k people) with my parents while recovering, and the doctors in the town here aren't exactly known for being world beaters and the hospital itself isn't the best (all draws were done in a public hospital). Back in capital I could go to a private lab but here it is not possible as it doesnt exist, so Im stuck with this lab. I even called the lab doctor and I told her that my dose increased, my diet is stable, it was 5 days since my last test of 1.8, but she couldnt shut up talking about how food can mess up INR values. In the end she kept repeating, you ate something that messed up your INR.

I read a lot of papers saying CoaguChek is quite reliable with a small margin of error, and to be honest I trust the CoaguChek value more than I do the public lab here... I will definitely do another check in a private lab as soon as possible.

But could this happen? Could a lab mess up my results? Or even, could CoaguChek mess up my results if the lab showed the correct value? I know that INR testing isnt an exact science, and that many factors influence day-to-day INR values, but these two were taken at maximum two hours apart (my lab test was taken around 9 in the morning, while the CoaguChek was taken at around 11 when I got home). I got my lab results at 1 PM.


Any tips/help?

Thank you very much!

EDIT:
I think I'll go to a private lab tomorrow to check my values again in another city, instead of the lab here.

there is a wide difference between the home check and the lab. Doubt there was any mistake done. And the timing our you testing at the lab and two hours later at home. You can try the private lab and test at home before the lab does it.

 

[pellicle]

there is a wide difference between the home check and the lab. Doubt there was any mistake done.

if this was true then the devices would not be legitimate measuring tools. There is not a wide difference in the main and if you are finding such you need to discuss it or investigate it ... antiphospholipid syndrome' is one such cause.

Many members here have attested to 0.2INR points difference regularly. Normally the issue actually lies with the lab.

I look forward to you posting your supporting data.

I react to posts like this because my goal is to support people with the truth, not agitate them with misinformation.

 

[thomas999]

I don't home check my inr,I depend solely on a hospital lab. The hospital is reputable and well known, and I trust them. That doesn't mean that mistakes can't be made, and if I get a report back that is questionable, I go and get it checked again. I guess I have been vigilant enough, it has been 35.5 years now. It always makes me wonder about the professionalism in the process of getting my INR checked, sometimes our livelihood is in the hands of other people.

 

[tom in MO]

Recall that it's in Bosnia, which isn't n EU nation and after the 1992 upheaval may not have much in the way of customer service mentality
https://en.wikipedia.org/wiki/Breakup_of_Yugoslavia

That's kind of insulting to Bosnians. 1992 is 30 years ago. Think of the difference in Europe between 1945 and 1975. Plus being in the EU is irrelevant to the medical care one receives in Bosnia. The majority of the world is not in the EU including your home of Australia.

 

[Timgander]

My Coaguchek is calibrated against the somewhat more sophisticated model they use at the clinic every 6 months or so (it was a condition of allowing me to self-test) and has always been spot on. I also have blood tests every month or so for something different (haematocrit) and have had very differing results from lab tests. One lab result came in at 0.56 which required a venesection but at the clinic they retested and got 0.51... (still had to lose 500ml).. And Hi Pellicle... I'm glad to see we are still both alive and kicking

 

[Protimenow]

I've run into multiple instances where the labs seriously mismanaged tests. All of the errors were on blood taken in doctor's offices or clinics, then transferred to a lab for testing. The blood was mishandled between the point where the blood was drawn, and the lab, where it was tested.

I've had two samples where the INR was probably normal, come back at 7 1 and 7.4.

A doctor that I had a few years ago told me that the lab reported my INR to be 5.4. He had a patient, whose INR was ALWAYS in range, also have a 5.4 test.

My meter said 3.1. TWO labs delivered results within 20% of my meter's results. I told my doctor that the lab tests were DEFINITELY wrong - they had been misproven by two labs and my meter.

These things happen. I doubt that the blood is treated in the same way that Pellicle's post said should be done.

LondonAndy's comment about lab results being acceptably close to CoaguChek XS results now makes me wonder if getting a blood draw at a reliable lab is worth the effort. (And it also makes me strongly consider abandoning my Coag-Sense from here forward, because it almost consistently delivers a result that's nearly 1.0 below the CoaguChek.)

 

[Protimenow]

Because it's just a device and devices often break down or malfunction and because we don't have any liquids to check the device at home for its accuracy. It is good to test it once a year, either by doing tests in a lab or with another device. Also, laboratories check their devices regularly, there is a relevant protocol.

Roche can't afford to have their devices 'break down.' Some clinics may do hundreds of tests a week. I have a model that's used in hospitals that may even do many more tests weekly.

The minimal number of tests that home testers perform in a decade may be less than what hospitals do in a few weeks.

Roche has engineered their meters and strips so that they stay accurate. Code chips that are included with strips provide adjustment values that are tuned to the strips so that the results are accurate. Quality controls are built into the meters and the strips.

There are no moving parts to wear out (unless you count the buttons that you push on the front and on the side. )

The strip guide may occasionally need cleaning - I don't know if a dirty strip guide will create an error message.

I used my first XS, which I bought used, for 8 years, with no problems.

I had a very used XS Pro that I also bought used. It started giving me error messages and I stopped using it. So - the meter told me that it was failing before I could get a result.

I suspect that if (not necessarily when) a meter fails, it won't let you run a test.

I am not convinced that the CoaguChek XS family of meters will fail - or that there are moving parts that will necessarily wear out - at least, not for quite some time. (I'm much less certain this is the case with a 'competing' meter that DOES have moving parts).

 

[pellicle]

My Coaguchek is calibrated against the somewhat more sophisticated model they use at the clinic every 6 months or so

Just to be sure, you mean compared to. Coaguchek can't be calibrated as supposedly the Coag-Sence can

 

[Protimenow]

Years ago, I sent my Coag-Sense meters to the factory for some kind of update.

The new meters are able to update their firmware via WiFi. I'm not sure WHAT the updates accomplished, but they CAN be modified by the manufacturer when updates are available. The CoaguChek XS doesn't have this capability (although I think that their latest and greatest may be able to download, in addition to uploading).

I don't know specifically if the Coag-Sense can be calibrated. They provide a pair of control tests with each box of strips, presumably to see if the meter is still accurate.