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Lab vs Home Test

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dick0236

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I often see posts where people are concerned that their meter differs from the one at the lab. I went, this AM, to my PCP office for my annual "well check" that is provided by Medicare. While having my blood drawn for general lab testing I asked if they would do a finger stick INR to check my meter against theirs. They use a CoaguchekXS identical to mine. They got a 3.7 @ about 11:l5am.

Earlier today, about 8:15am, I self-tested at home on my CoaguchekXS and got a 3.4.

Neither my doc nor I were concerned about the difference in INR(3.4 vs 3.7)........goes to show how different meters and probably some "metabolism differences" over the 3 hours between tests might affect INR readings.

I crosscheck my meter against my docs every year or two and they have always been close to one another........but never identical:cool:
 
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Eva

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It’s good practice to check one‘s machine‘s against the doctor’s. My last machine‘s results were way off last March from Lab’s and Dr’s office...It was breaking down. Then it stopped working completely.
stay healthy and safe.
 

LondonAndy

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I agree Dick - this coming Monday I shall be going to my local anticoagulation clinic to check my meter against theirs. I normally do it every 6 months or so, but because of Covid this time it will have been almost a year. I will take my own reading in front of the nurse, so that there is no difference in timing of the blood samples and also if there was any doubt about my technique it could be picked up then. Sometimes they do a check on their meter, more usually they do a blood draw, but either way there has never been a difference greater than 0.2
 

Freddie

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FWIW
A lab tech told me that they take 3 samples from your blood draw then average out the clotting time and allow a 0.2 or 0.3 (+/-) in the reading.
 

pellicle

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I crosscheck my meter against my docs every year or two and they have always been close to one another........but never identical:cool:
Great topic for a post and of course always timely for home testers and self mangers.

Dick is one of those members who began taking warfarin before even the concept of INR existed, and has its history in the move from Prothrombin Time via Prothrombin Time Ratio to eventually the International Normalised Ratio we all know but are probably not familiar with what it means.

Dicks observation cuts to the heart of why we take warfarin: to reduce the negative effects of coagulation triggered by our artificial heart valves.

So this is the intention of our taking warfarin, to keep ourselves in a goldilocks zone where we are not too little and not too much anti-coagulation managed. This is ultimately the goal of the clinical practice, to make sure we don't have any uncontrolled bleeds and to make sure we don't suffer strokes from thrombosis.

This is pretty well worked out now and has quite a wide range of INR (which I'll place at the bottom of this post).

Especially for the OCD, its important to recognised that theses numbers are not like measuring a piece of steel with a micrometer at a standard controlled temperature, they are much more rubbery than that. Meaning that there is number differences which are not significant to the clinical goals: clinical significance reflects its impact on clinical practice.

So obsessing over am I 2.4 or 2.5 or 2.6 is not of significance on outcomes. This is why we've moved from "ranges" to targets (well slowly moving), where just like target practice you have a bullseye that you aim for and rings away from that indicating how far off target you are (the whole thing is not the goal).

So you can see below that the bullseye of clinical goldilocks is quite wide, and well within the capacity of the tools we have to make sure we remain inside the boundaries of safe INR.



Best Wishes
 

LondonAndy

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I had my six year old CoaguCheck XS "calibrated" at my anticoagulation clinic today, as per my earlier post. (IE I took a reading on my machine and they took one on theirs, seconds between the two tests).

My machine reading was 2.8, theirs (the bigger CoaguChek machine for clinic use) was 2.7. All good for another 6 months at least, though frankly I would expect an error message on my machine if it was going wrong rather than a different result. But doesn't hurt to check.
 

Protimenow

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Calibration suggests that some change or adjustment is made to a meter (or whatever is being calibrated) to make it 'accurate.' What you did, LondonAndy, is just to compare the results from the two meters. If, six months from now, you get a major difference between the two meters (I'm thinking of a difference of 1.0+, would you get a new meter?)
 

LondonAndy

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Calibration suggests that some change or adjustment is made to a meter (or whatever is being calibrated) to make it 'accurate.' What you did, LondonAndy, is just to compare the results from the two meters.
I agree, and that is why I put it in quotes on this second post in this thread - in the first post I said exactly what you say here. For some reason "calibration" (note the quotes) is what the anticoagulation clinic calls it.
 

vitdoc

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pellicle

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I doubt there is any likelihood that the meter changes with time
agreed ... rather like a CD player just reads the data and over time the CD's still sound the same
(just wondering, is there anyone here who doesn't know what a CD is? I mean I've gone through 8 Track, LP, Cassette, MiniDisk, CD, MP3 and now just streaming)
 

Eva

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My Coagucheck Xs broke after 12 years. Before breaking, it gave me results that differed a lot from the lab, then it gave me “error” messages when I inserted a strip. I changed the strip, error message again. Bought new strips with a new chip code, I still had a few error messages Hubby changed the batteries, it improved for a while, but *died* at the end...no messages...nothing. Roche asked me to return the machine and that’s when I lost my 2 chips!
 

Protimenow

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agreed ... rather like a CD player just reads the data and over time the CD's still sound the same
(just wondering, is there anyone here who doesn't know what a CD is? I mean I've gone through 8 Track, LP, Cassette, MiniDisk, CD, MP3 and now just streaming)
What? No Four Track? (These weren't out for very long -- the cartridges didn't have a wheel to drive the tape - so a wheel went up into the cartridge to propel it. 8 track tapes got twice as much music per tape (who cares about sound quality in a car, anyway?) and had the drive wheel inside the cartridge.)
 

ATHENS1964

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Τoday I had to do blood tests and I also did INR. The tests were performed in a new laboratory and not in the usual one.
The LAB gave 2.37 and the coaqucheck 2.5
I would like to ask if 2.5 can be up to 2.9 or up to 2.54 and then the measurement would change to 2.6?
It would be nice to know that roche depicts the result with two decimals for example the 2.37 how roche write 2.3 or 2.4 ?
 

LondonAndy

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I think you are worrying about a level of accuracy unnecessarily, Athens: it is a measurement of something that fluctuates slightly all the time, and as long as the difference between a lab and your meter is not too great (for me that means a difference of +/- 0.2 or less, others may vary) I personally am content. In six years of home testing I have never had a reading with a greater difference than 0.2, but if I did I would retest to confirm.
 

Protimenow

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I'm not exactly sure why the labs reduce this to decimal accuracy. If they repeat the test on the same sample, they may get a result that's slightly different.

I would be satisfied if my INR was even .4 or .5 different -- the only time when I'd worry is when my INR (lab or meter) is 2.0 or below.
 

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