Home vs lab (stago, sysmex) INR values

[aortic3]

Long time lurker, first time poster.

Quick background on me:
- Born with bicuspid aortic.
- Age 9: commissurotomy of aortic.
- Age 24: Ross Procedure.
- Age 46: Mechanical Aortic and Pulmonary.
- INR Range: 2.5-3.5

I have been on Warfarin for 10 years, check my INR 2-3 times a week with Coaguchek. My coaguchek has reliably been 15-20% higher than the lab. Basically the higher the INR, the bigger the variation. The variation is consistent. I keep a spreadsheet with statistics of every Lab vs coaguchek INR and can easily map what my INR is.

Question #1: Am I the only one whose coaguchek reports consistently higher than the lab every time? Does anyone have an explanation why?

For years I went to the same local hospital for an INR check. They used a Stago machine. Stago measures with viscosity based detection. It detects clot formation by measuring changes in the blood's viscosity rather than relying on optical methods.

One day that local hospital switched from Stago to Sysmex. Sysmex measure coagulation with a photo-optical detection method. The Sysmex measurement matches my coaguchek measurement (aka 15-20% higher than stago)

As an experiment one day I went to a hospital with Stago (INR=3.3), my local hospital with Sysmex(INR=.4.1). Both results were where I expected them. Sysmex was 20% higher than Stago. Both results were reported to my Warfarin provider which made for a fun day on them advising me on how to manage my warfarin that day.

FWIW, Labcorp uses Sysmex.

It's concerning that different machines used by hospitals and labs can give entirely different INR #'s. Sysmex being 15-20% higher than stago. I repeated this experiment a few times thinking maybe the Sysmex machine wasn't calibrated. But the Sysmex machine was consistently 15-20% higher than Stago. Which one do I believe?

I'm not sure what my question is here. Kinda wondering has anyone else had experiences like this? Or have detailed knowledge of Stago vs Sysmex?

Thanks.

 

[MdaPA]

Am I the only one whose coaguchek reports consistently higher than the lab every time?

No, others have reported as well. See some past discussions below:

https://www.valvereplacement.org/th...ween-coaguchek-xs-and-lab.888345/#post-912960

https://www.valvereplacement.org/threads/coag-sense-versus-coaguchek-xs-and-labs.887606

Does anyone have an explanation why?

I like pellicle's quote we're "....not measuring a piece of steel".

 

[Chuck C]

Welcome to VR!

I home test with the Coaguchek xs. When I test at the lab, to make sure my self test device is accurate, I use Quest Diagnostics. I test with my Coaguchek within 10 minutes of my blood draw at the lab and it has always been either exactly the same reading or off by 0.1.
I do have a high degree of confidence in my Coaguchek.

 

[Beach77]

@aortic3 Question #1: Am I the only one whose coaguchek reports consistently higher than the lab every time? Does anyone have an explanation why?

Yes, I have the same issue. I go to the lab every 6 weeks. The lab is onsite of a teaching hospital and the results are given to the Coumadin Clinic within one hour. It's a recurring Stat order. My INR range from my doctor is 2.5 to 3. However, I test weekly at home with a Coaguchek XS that I bought off Ebay.

What I see, is the higher the INR, from the lab is, the larger the difference from my meter. The lower the INR from the lab, the meter result is closer. No clue why. I do wonder if it has anything to do with the blood cooling quicker on the strip?

With this in mind, I personally keep my home range to 2.9 to 3.5. I don't worry about the difference. The clinic is aware I have the meter for my personally testing but they only go by their lab results. It's been 4 years since my surgery. The clinic gives me my Warfarin, we go by the lab results. I'm ok with that.

Here are examples of my readings:

Self	Lab
3.0	2.4
3.5	2.7
3.2	2.6
2.5	2.2
2.5	2.1
1.3	1.2

(FYI...I was on Lovenox injections when my INR was 1.2)

I think @Protimenow has a lot of info on this subject too.

 

[pellicle]

Hi and welcome from Australia

Long time lurker, first time poster.

Quick background on me:
- Born with bicuspid aortic.
- Age 9: commissurotomy of aortic.
- Age 24: Ross Procedure.
- Age 46: Mechanical Aortic and Pulmonary.
- INR Range: 2.5-3.5

similar background, I had my first (similar procedure) at 10 and my second at 28 (which was a homograft) and my third at 48 which was also a mechanical (but only the Aortic) and an aneurysm fix with a Bentall

I have been on Warfarin for 10 years, check my INR 2-3 times a week with Coaguchek.

similar here

My coaguchek has reliably been 15-20% higher than the lab.

mine has not been that, its been on average (over a quite few readings) 0.1 INR units variant (0.04 if I leave negative and positive difference and 0.09INR units if I take absolute numbers of difference)

Basically the higher the INR, the bigger the variation. The variation is consistent. I keep a spreadsheet with statistics of every Lab vs coaguchek INR and can easily map what my INR is.

excellent work!

Question #1: Am I the only one whose coaguchek reports consistently higher than the lab every time? Does anyone have an explanation why?

no you aren't and the answer is that its down to the reagents ... its not like measuring a piece of steel, its an indirect measurement with a bunch of factors involved, so its a rubbery thing. Yes there are ISI corrections but you know, its never perfect and its a cloudy goal not a single point.

For years I went to the same local hospital for an INR check. They used a Stago machine. Stago measures with viscosity based detection. It detects clot formation by measuring changes in the blood's viscosity rather than relying on optical methods.

first thing, this is an error promoted by the misuse of "blood thinners" and there is no actual change in viscosity, it is properly called Anti-Coagulation Therapy (ACT) and there is a class of drugs which effects viscosity and we aren't on that. So every medical person who uses the term "blood thinners" is basically making a mistake.

Next exactly as you lead to, the methods of determining the level of coagulation there are optical methods and there are electronic methods. Here is a google search on the Stago and i-STAT devices and some basic details about them

Some of the links provided by Google in that
https://pubmed.ncbi.nlm.nih.gov/208...s: Accuracy was superior with,INR (p < 0.001).

https://pubmed.ncbi.nlm.nih.gov/240...s and factors related to performance variance.

https://fritsmafactor.com/ptinr-i-stat/

One day that local hospital switched from Stago to Sysmex. Sysmex measure coagulation with a photo-optical detection method. The Sysmex measurement matches my coaguchek measurement (aka 15-20% higher than stago)

yep, see my above point about "the rubbery thing" ... this is built into the idea of why we have a range not a single number (among other reasons).

As an experiment one day I went to a hospital with Stago (INR=3.3), my local hospital with Sysmex(INR=.4.1). Both results were where I expected them. Sysmex was 20% higher than Stago. Both results were reported to my Warfarin provider which made for a fun day on them advising me on how to manage my warfarin that day.

I love that

It's concerning that different machines used by hospitals and labs can give entirely different INR #'s. Sysmex being 15-20% higher than stago. I repeated this experiment a few times thinking maybe the Sysmex machine wasn't calibrated.

not really ... the key point is that its a range and the term "clinically significant" is important. Its not like a bolt and a nut where you must have the same diameter and threadpitch; or it won't work.

But the Sysmex machine was consistently 15-20% higher than Stago. Which one do I believe?

Man with one clock thinks he knows the time man with two clocks does not know the time

The answer lies in this study and its data

URL for study
http://jamanetwork.com/journals/jamainternalmedicine/fullarticle/415179

here you can see where (colours added are mine) between 2.5 and 3.4 is basically the same level of risk actually measured by outcome.

HTH

 

[pellicle]

I like pellicle's quote we're "....not measuring a piece of steel".

and I've actually repeated it ... before I read this. I like it too ;-)