Have any of you compared the results from two (or more) different meters?

[Protimenow]

In a perfect world, our blood meters would give us INRs that perfectly match the results of a blood draw. In this world, it wouldn't matter which meter was used -- all would give identical results.

The world is far from perfect.

A few years ago, I had a concussion, and the ER blood draw gave me a result that was almost exactly the same as my test using my ProTime meter a day earlier. I trusted this meter.

When I got my InRatio, the results were close to those from my ProTime. I trusted it.

A few months ago, I had a stroke -- fortunately, one from which I recovered completely (I think) -- in part because I relied on my meter to give me an accurate INR.

I'm now testing with two meters - my InRatio and a ProTime or ProTime3. The results are about a full point apart (recently, my InRatio gave me a 4.1 and a ProTime gave me 3.1). When these were last compared to the lab, the actual lab value was almost in the middle.

Roche claims that their CoaguChek XS is '97% accurate' and a lab is '99% accurate."

I wonder if this is true.

I know that some of us have switched meters over the years. I'm wondering if any of you who HAVE switched meters have been able to compare your values - recorded on one or meters - minutes apart, and what the results were. I'm also wondering what the lab values were for tests on the meters that were taken at nearly the same times as a blood draw.

If any of you have had experiences comparing two meters, or meters and blood draws, I'd sure like to read about them.

 

[Protimenow]

I just tested again - 2.8 on the ProTime, and 3.8 on the InRatio. I had a blood draw this morning, and I'm about to have one again in 30 minutes or so (different lab). I have a friend with a CoaguChek XS - and he's pretty confident that its results are pretty close to lab results.

Maybe one day I'll have an XS and find out for myself.

But, again, which do you trust? Have ANY of you compared meters. (I've compared two InRatios to each other, and to ProTimes to each other -- the results of each machine are pretty close to the other machine - but nowhere near the other TYPE of machine).

 

[newmitral]

Hello Protimenow,

I have not compared test results from 2 different types of meters, but I have compared test results from two meters of identical type.

Over the past several months, I have compared my own INR results from two different Inratio-2 machines. One is my "official" Inratio-2 machine supplied to me directly by Alere/Philips, and the other is a second Inratio-2 machine I purchased on Ebay.
Using different lots of test strips, with different batch codes in each machine, the two machines consistently agree within +/-0.1 in INR for the tests I have made over the past few months. I have tested just a few minutes apart on the two machines. I have made enough comparison tests that I'm confident my Ebay purchased machine is consistently giving the same test results as the Alere/Philips supplied machine.

I do not yet have enough test comparisons with venous blood draw lab INR tests to conclude whether the Inratio-2 machine is consistently different, either high or low, from the lab test result.
Perhaps in another year I will have enough test points to reach a conclusion on that.

This was discussed at great length in the thread:
www.valvereplacement.org/forums/sho...s-ground-truth-home-meter-or-lab-venipuncture
in which I believe you were also a participant.

As noted in that prior discussion, the lab draw tests are the "gold standard" of accuracy, and the meter tests should be within an (unfortunately fairly broad) known tolerance range from the lab test. The tradeoff with the home test machines is a hopefully small/acceptable increase in test result error for the convenience and increased frequency of testing versus the venous blood draw lab test. My personal opinion is that, for me, the increased frequency of testing (weekly for home test versus monthly for lab test) outweighs the increase in test error. Everyone's situation is different, and my own INR fluctuates dramatically week to week, so the increased frequency of home testing is more important for me than a few tenths in INR absolute accuracy.

Your own mileage may vary.

 

[Protimenow]

I"m sure that I participated in the thread that you mentioned.
A few months ago, an Alere rep told me to 'trust the lab.' That's what I'm doing now -- I wish that I had less faith in the accuracy of my meter a few months ago, when my low-end of range meter readings actually had my INR down below 2 for quite a while. Had I been able to compare to a blood draw, I would have realized that the InRatio is probably consistently .5-.7 higher than the lab. Also -- there was a thread where a predictive formula was given for converting InRatio to lab results. This information came too late to help me.

I've also compared InRatio (bought on eBay) and InRatio2 (directly from Alere), using the same lot of strips, and the results also agreed (or within .1 of each other, as you report).

It's disappointing that, if Alere knew of the fairly reproducible difference between InRatio results and actual lab results, that they either don't upgrade the meter's firmware to automatically make that adjustment (there are probably too many meters to do this), or inform the Anticoagulation clinics and home testers that the meter fairly consistently reports INRs that are .5 - .8 (or so) higher than lab results and to adjust accordingly. IF this deviation is true for ALL patients, and ALL InRatio meters, getting this information out would help the next person who trusts the meter enough to spend weeks below 2.0.

Like you, I prefer testing weekly. I'll probably continue with ProTime and InRatio (one incision, two tests) until I run out of ProTime cuvettes.

(Today, there were some interesting tests done. I had a blood draw at one clinic, and another blood draw at a hospital, and two meter tests. It'll be interesting to see what the labs have to report).

Thanks for responding.

 

[Protimenow]

I continue to get further confirmation that my InRatio is less than accurate - but that it may be reliably about .6 or .7 higher than lab tests. On Monday, I tested with my InRatio 2 (3.8), and my ProTime (2.8). I got two blood draws at two different labs that same day. One lab had a value of 2.97. I hope to have the value from the other lab later today.

When I compared the InRatio and the InRatio 2 with the same lot of strips a while ago, I got nearly the same results each time. The variance from lab values is fairly consistent in both meters - but I'm not sure if the error IS consistent. A few months ago, there was a post with a method for converting the InRatio results to actual lab values. I'll have to give that a try -- although it would have been good if HemoSense (which developed the InRatio) built that algorithm into their meter before they released it to the public.

I'm still curious about the CoaguChek XS. If I can get my hands on one, I'll eventually report on my experience with the accuracy of the XS.

I'm still not entirely convinced of the accuracy of the ProTime meters, but I feel more confident with their results.

 

[Protimenow]

Wow.

I just got a call from the clinic that ordered the OTHER lab to do a blood draw. THEY REPORTED A 3.6. The hospital lab had a 2.97 -- my meters reported a 2.8 (ProTime) and 3.8 (InRatio 2) -- all within minutes (the 3.6 lab and the meters) or a few hours (the hospital lab) of each other.

I'm inclined to trust the hospital lab - although the other lab's 3.6 puts it very close to my InRatio.

Do I assume that the hospital lab has been botching the tests (or, at least, botching THIS test), or that the other clinic has botched its handling of my blood? Is my InRatio now somewhat more accurate (because it reported results that were closer to the other lab?).

If labs can be .63 apart from each other, WHICH LAB CAN YOU TRUST? I'm thinking that the hospital lab knows how to handle the blood and runs the tests fairly soon after drawing the blood -- and that the blood at the other facility may have been held for a long time, possibly not tested with the right reagents, or who knows?

If LABS don't have similar values, then what can you trust?