INR difference between lab and my Coagucheck

[Eva]

Hello. Yesterday, I had lab work at my doctor’s office including INR testing.
I had my machine with me. I tested my INR pricking my finger.

My Coagucheck XS result was 3.8.
Lab result is 2.5!!! Big difference!
WHAT’s you advise. My machine is about five years old. Thanks in advance.

 

[jeffp]

Old saying: a man with 2 watches never knows what time it is. This was before GPS synced phones.
I’ve had similar INR experiences. I tend to trust the XS more than the labs for INR. I know how the strips are handled and stored. Blood draws can sit for a while, be stored too hot, reagents can be old (storage issues can affect those as well), the preservatives in the tube can be too much or not enough, etc. I once had 2 lab draws back to back with an INR difference of a bit over 1 unit.
If its routinely off, and by the same amount(ish) in the same direction, from different labs, then I’d be a looking at the XS or strips.

 

[pellicle]

Good Morning Eva

My Coagucheck XS result was 3.8.
Lab result is 2.5!!! Big difference!
WHAT’s you advise. My machine is about five years old

well that is rather a large difference. I would (as you are) want to investigate that.

3.8 would sort of encourage me to steer down however with the guidance of 2.5 as a "second opinion" in the data I would not.
So to clarify my understanding:

1. at the Dr office you had a vein draw and you used your coaguchek
2. the INR from the coaguchek was noted (either you wrote it down or just used the machine memory of that)
3. when the lab results came in they notified you and you compared the two

So assuming that's what happened I would be interested in a few things to clarify this (no order this time)

• clarify exactly what the lab process is; do they use a machine like an I-Stat or a STAGO STA-R automatic coagulometer or do they do it the "from scratch" old fashioned way of centrifuging out the plasma and applying this to the traditional reagent approach.
• I'd want to repeat the test to see if another test shows a similar result

Just for your info from the Stago company page.

Stago employs a unique, mechanical viscosity-based detection system in all its systems offering a reliable-result guarantee, since measurements are not affected by optical interference. In addition, this detection system offers optimum sensitivity for weak clot detection.​

its worth noting that the Coaguchek does not use optical methods for determining coagulation. The CoaguChek uses "amperometric electrochemical" methods for determining the time to declare the point of "coagulation" to stop the timer. A good summary of this and other methods is here (link). So this may explain the differences.

Its interesting isn't it, how many ways to measure a piece of string are there?

Of course its too early to call this but the development of Antiphospholipid syndrome could be the cause of a prolonged INR result (as you seem to be seeing). I would also ask your Dr about this possibility and test for that.

I would not alter dose at this stage because we don't know the answers to the above questions.

Some additional readings on the topic
from this link:

There is a warning on the pack inserts for the Coaguchek XS testing strips which states:​

“Antiphospholipid antibodies (APA) such as the Lupus Anticoagulant (LA) may falsely prolong coagulation times ie. they may cause false high INR values and false low values. Where APA are known to be present, it is imperative that a result be obtained using an APA-insensitive laboratory method for comparison”.​

https://www.mayoclinic.org/diseases...holipid-syndrome/symptoms-causes/syc-20355831

 

[Eva]

Old saying: a man with 2 watches never knows what time it is. This was before GPS synced phones.
I’ve had similar INR experiences. I tend to trust the XS more than the labs for INR. I know how the strips are handled and stored. Blood draws can sit for a while, be stored too hot, reagents can be old (storage issues can affect those as well), the preservatives in the tube can be too much or not enough, etc. I once had 2 lab draws back to back with an INR difference of a bit over 1 unit.
If its routinely off, and by the same amount(ish) in the same direction, from different labs, then I’d be a looking at the XS or strips.

Thank you. What you say makes sense especially that my blood was drawn around 4:30 p.m. so, not sure when it was delivered to the lab. I’m going to check about this.

 

[pellicle]

PS:

lastly which strips are you using? There are now two and I'm told by Roche (when I asked) if the differences are worthy of note. They said no.

and the ones for the INRange

note the difference is subtle

HTH

 

[Eva]

Pellicle, thank you. It’s a big difference and it scared me about how to adjust my dose. But since I can go up to 4, and after reading @jeffp’s message, I may continue the same dose until I call the UCLA lab and ask them what method they used and discuss this. Thanks for the hint.

ANSWERING YOUR QUESTIONS IN BOLDED CAPITAL LETTERS :

1. at the Dr office you had a vein draw and you used your coaguchek. YES!
2. the INR from the coaguchek was noted (either you wrote it down or just used the machine memory of that). INR WAS NOTED… NOT FROM MEMORY. WROTE IT DOWN AND ITS STILL IN THE MEMORY!
3. when the lab results came in they notified you and you compared the two. YES! I always receive lab work test results on-line!

THANKS AGAIN.

 

[Protimenow]

Old saying: a man with 2 watches never knows what time it is. This was before GPS synced phones.
I’ve had similar INR experiences. I tend to trust the XS more than the labs for INR. I know how the strips are handled and stored. Blood draws can sit for a while, be stored too hot, reagents can be old (storage issues can affect those as well), the preservatives in the tube can be too much or not enough, etc. I once had 2 lab draws back to back with an INR difference of a bit over 1 unit.
If its routinely off, and by the same amount(ish) in the same direction, from different labs, then I’d be a looking at the XS or strips.

Interestingly, the ISO (or a different standards organization, I can't remember whh) says that the INR is accurate within 20%.

If you subtract 20% from the 3.8 (giving you 3.04) and add 20% to the Coagchek's value, 3.0, the results are almost the same.

If your blood draw was done at UCLA, was it at one of their clinics (?). It may be possible that the sample was mishandled.

If I encountered the same difference (and I DID run into large differences between labs a few years ago), I would trust my meter more than most labs.

FWIW -- My CoagSense meter always gives me a result that may be up to 1 point higher than the XS. I used to trust the CoagSense more than the XS because I feel safer avoiding an INR that is too low than I am avoiding an INR that is too high.

 

[LondonAndy]

I am with the general view, that I tend to trust my CoaguChek more, for the reasons given by @jeffp

 

[Eva]

Pellicle, the top one.

Interestingly, the ISO (or a different standards organization, I can't remember whh) says that the INR is accurate within 20%.

If you subtract 20% from the 3.8 (giving you 3.04) and add 20% to the Coagchek's value, 3.0, the results are almost the same.

If your blood draw was done at UCLA, was it at one of their clinics (?). It may be possible that the sample was mishandled.

If I encountered the same difference (and I DID run into large differences between labs a few years ago), I would trust my meter more than most labs.

FWIW -- My CoagSense meter always gives me a result that may be up to 1 point higher than the XS. I used to trust the CoagSense more than the XS because I feel safer avoiding an INR that is too low than I am avoiding an INR that is too high.

The result of the lab was 2.5.
Blood was drawn at my doctor’s office at 4:30 pm. Don’t know what time it was picked up and sent to the lab.

 

[ATHENS1964]

In order to check the inr range, I do the examination in a specific laboratory which is certified by European organizations, it is one of the largest that exist in Greece and they give me the result very quickly in about 3-4 hours. The comparison always doesn't have a difference greater than 10%, once only at the beginning when I was out of the hospital just 20 days after the operation, I did the measurement in a neighborhood lab, the difference was about 30%, my doctor told me to I repeat it in another laboratory and the next time I repeated it, the difference was 10% - 13%
In the link is the laboratory I use in a central part of Athens and very close to my work.
https://bioiatriki.gr/en/diagnostic-centers-network/bioiatriki-ampelokipi/

 

[Protimenow]

In 2019, I had my blood drawn at my rheumatologist's office. I was told that the INR was 5.2.

I didn't believe it. When I got the result from the doctor, I did my own search for an accurate result.

The UCLA lab gave me a 3.6. Another doctor's office gave me a 3.5. My CoagSense gave me 3.0 (this meter is ALWAYS low, so the result may also have been around 3.6 or 3.7).

I told my doctor that his lab results were wrong -- he thanked me because he had another patient with a high INR that didn't seem right. I didn't ask about the way blood samples were handled in his office but probably should have.

Labs don't always get it right.
-

 

[Superman]

I had a recent 3.5 (meter) to 2.7 (lab) result. But they were a day apart and my meter test was in the afternoon and the lab in the morning. Not very controlled so I didn’t put a lot of stock into it and wouldn’t change my dose for either one.

 

[Eva]

@pellicle ,
I remembered this morning when this happened before, Roche contacted UCLA lab on my behalf to check which method they use! It was the same and I was advised the buy a new one which I used at the doctor’s office. But, I’ll still call UCLA lab.

 

[Protimenow]

Are you saying that the UCLA lab told Roche that it was using the XS? This still doesn't account with issues related to how the sample was handled. If UCLA was actually using a different method and didn't understand what Roche was asking, the lab may have been using a different reagent, which may also give a different result.

If it was me, I wouldn't dump my meter before testing your meter side by side, using the same strips and code chip, against the meter at your doctor's office.

 

[tom in MO]

I'd suggest asking whoever prescribes your warfarin to assess the disparity and suggest a course of action for your dosing and whether or not you should continue to believe the meter over the laboratory result. I would also contact the meter supplier and tell them about the disparity and ask what you should do concerning future readings.

 

[Timmay]

This might not help Eva but I wanted to post some results here for future readers.

I have 3 Roche CoaguChek meters. All 3 test within 0.1 INR.

Additionally, I always always always validate new test strips against my existing test strips by doing comparison tests on the same day/time (different fingers of course: old batch with one finger immediately followed by a strip from the new batch using a different finger). So far, after a year of testing at least twice a week, I can say that the strip batches with different code chips have ALWAYS been within 0.1 INR (with 0 difference happening more than the 0.1)

So - for me - the CoaguChek XS and the strips are extremely consistent.

I have done 1 blood draw comparison test thus far. The blood draw from LabCorps was 2.1 while two of my meters agreed at 2.5.

Oddly enough, I had a blood draw today for INR. I will update this post with those specifics when I receive them.

Long story short, I trust my meters way more. I can’t guarantee how they’re handling my blood.

 

[Eva]

I totally agree that our meters are more reliable! After I returned home from the doctor’s office, I tried to remove the bandaid off and there was still some blood (like a wet drop ) there. I put a new band aid and a newer one after a few minutes! This to me confirms that my INR was 3.8 (my machine’s result).

 

[Eva]

Are you saying that the UCLA lab told Roche that it was using the XS? This still doesn't account with issues related to how the sample was handled. If UCLA was actually using a different method and didn't understand what Roche was asking, the lab may have been using a different reagent, which may also give a different result.

If it was me, I wouldn't dump my meter before testing your meter side by side, using the same strips and code chip, against the meter at your doctor's office.

No. The lab didn’t use XS…it used then the same reagent! I’m keeping my meter!

 

[Eva]

I'd suggest asking whoever prescribes your warfarin to assess the disparity and suggest a course of action for your dosing and whether or not you should continue to believe the meter over the laboratory result. I would also contact the meter supplier and tell them about the disparity and ask what you should do concerning future readings.

Thank you. I’ll do.

 

[Protimenow]

The lab did NOT use the same reagent as the XS. There is probably NO reason to contact Roche about the result -- they'll talk to you but this will be a waste of your time and theirs.

Your doctor probably knows little that's relevant about INR management. I wouldn't rely on an answer from him or her.

Although the results seem to be far apart, as I noted in a previous message, they're within an acceptable margin of error.

The next time you use the lab for comparison, it will be interesting to see how the results compare.

If you DO contact Roche, I would be interested in hearing their response.

(I have the CoagSense meter, and it is ALWAYS lower than the XS. I rarely use the CoagSense and prefer the meter (the XS) that has become a standard of self testing in America, and probably any country where it's sold.)