Accurate meters?

[Protimenow]

I'm 21 years post-op. Before 2009, when I finally got a meter, my lab testing was infrequent and somewhat erratic. In retrospect, I was fortunate not to have any (known) TIAs or major hemorrhaging issues. In retrospect, I was probably pretty foolish not to stay on top of my INR.

In 2009, I got a ProTime meter and started testing. I used the 3-channel ProTime cuvettes. The one time I had the result correlated to a lab, a day after testing, the results were almost identical.

I upgraded from a ProTime Classic to a ProTime 3, and results on both machines were pretty close matches.

I have also had a CoaguChek S, and used the last batch of strips, and I also got an InRatio.

In April, I relied on my InRatio to be lab accurate, but didn't compare it to a lab. I had a TIA, and later found out that the InRatio was reporting considerably higher than the lab values. A 2.7 on the InRatio was a 1.7 at the lab (in fairness, there was a considerable delay between the two tests), but subsequent tests using the InRatio were always higher than the lab.

I had two blood draws at two different labs, within hours of each other, and got two considerably different INRs - a hospital lab gave me 2.9, a clinic lab resulted in a 3.6.

There has been writing on this forum about lab problems in handling blood samples, and in problems with meter accuracy.

I bought a Hemochron Signature meter on eBay - the kind they use in the Anticoagulation clinic - but may not be able to use it because it requires electronic QC testing. (I didn't pay much for the meter, so it wasn't a total waste).

Roche claims that the CoaguChek XS has a very high correlation with lab values. (I'm thinking that if you go to enough labs, you can find a good match). I was told by a vendor that the InRatio has the worst correlation to lab values of the three meters that are readily available.

I started using 3-channel cuvettes for the ProTime machine, and its results were a full point lower than the InRatio - and quite a few tenths below lab results. I reported this to ITC, which makes the strips, and they didn't seem to care.

Last month, they issued a recall on the 3-channel strips (possibly, in part, because I may not have been the only one to report the error).

I just learned that the five channel ProTime strips are supposedly as accurate as the Hemochron (and, by extension, nearly as accurate as lab results). I will probably return my recalled strips, and try some replacement five channel strips.

So - my question is this:

We are betting our lives on the accuracy of our meters (or the labs) whenever we test our INRs. We make dosing (and maybe dietary) decisions based on these results.
Is there a meter that is the most accurate of the four or so that are available? Have many of you compared your meter results with lab results?

I had a minor TIA from which I think that I've completely recovered - but I don't want another. As a committed self-manager of my anticoagulation, I want to be able to use the most accurate (or most reliably inaccurate) meter available. (When I say 'reliably inaccurate', I'm talking about a meter that may ALWAYS be a certain percentage higher than a lab -- by subtracting a predictable error, you can estimate accurate lab values).

Any ideas?

 

[tom in MO]

Relax. You worry too much about your INR and your machines.

You expect an INR measurement to be an exact measurement, it is not, whether it be by laboratory or by machine. That's one of the reason's it is "normalized." An INR measurement does not measure a "thing" such as a ruler measures length. It measures a rate of reaction...clotting time for a specific size and age of drop.

Due to this, there is no "correct" INR. There is only a desirable range. This range can change by valve and over time as more is known about your valve and its relative risk to coagulation problems.

Your post here and elsewhere indicate that you don't trust the manufacturers or the laboratories. If so, you will never be happy.

You have to trust something to measure your INR. However, you will never find the "full story" on meters or laboratories. This is for many reasons, some of it is proprietary information (labs and manufacturers have the right to protect their intellectual property), some of the information is not available on free search engines, but most of all the info is not available due to the fact that to generate the data you want (e.g. statistically significant comparison of all manufacturer's meters and all types of testing laboratories) is very expensive and who (besides you) would pay for it?

 

[Protimenow]

Actually, no, I'm not looking for an exact number, but it's good to know how a meter (or lab) results relate to each other. I've mentioned 'reliability' before -- if my meter is always an approximate amount higher than the lab, then I'll expect that it's possible to get a general feel of what my approximate INR really is. ITC used to represent their ProTime as being very close to lab results - but this recent recall of strips (perhaps partially resulting from my phone call telling them that their results were considerably lower than lab tests) shows that even THEIR quality controls can be off.

Personally, I'm probably more comfortable with being a bit above range than with being below 2.0 Although I don't have a knee jerk response to an INR below 2.0 and run for the Lovenox, I'll probably increase my dose until I'm comfortable that it's above 2.0.

It would certainly be nice to have SOME method of accurately determining an INR.

 

[pellicle]

While it is attractive to wish for such accuracy, reality is that measurements of this nature do not conform to engineering practice.

You can measure micrometers but getting the same INR twice to an exact number just is pushing the boundaries of diminishing returns.

 

[Protimenow]

I like to know that my INR is sort of in range. I've been assuming that my InRatio was always a bit high, and satisfied that anything above 2.9 or so was good.

Last week, I got 5 channel ProTime Cuvettes that replaced the recalled 3 channel cuvettes. (I'd like to think that my call to ITC helped to convince them that their strips were faulty). I was also told by a ProTime dealer that the 5 channel cuvettes were very close to lab results - and similar to the results of the Hemochron, which ITC also makes.

Parallel testing with ProTime 5 channel cuvette and InRatio was reassuring - the InRatio gave me a 3.1. The ProTime result was 2.9.

I'm pretty confident that I'm in range. I may do a few more parallel tests to see if I get results that are also fairly close, and may do occasional blood draws for another data point. (Blood draws are also not always reliable - there's variance from facility to facility).

(One nice thing (if nice is the right word) about the ProTime and InRatio testing is that I only have to make a single incision. The ProTime comes with a lancing device that makes an incision that is large enough to get blood for both machines. The ProTime doesn't use the first drop of blood -- that goes to the InRatio. After wiping off any remaining blood, I get the blood into the incision device (Tenderlette) and, from there, to the ProTime).

The ProTime meter is big when compared to the InRatio. The 3 channel and 5 channel cuvettes take more blood. Testing may be a bit trickier. It takes up to two minutes or so to get results. When a cuvette has expired, the machine won't use it. When I got my InRatio, I thought that I was through with the ProTime. For a while, I will probably use both. If the InRatio gives me a questionable result (usually higher than expected), I'll probably use the ProTime to double check. In spite of its larger size, and the tests being less easy to run, it may be more accurate than the InRatio (in my experience, if the cuvettes are okay).

Not having a CoaguChek XS, I can't comment on its accuracy versus the ProTime or the lab.
Roche is not at all interested in enabling me to make these comparison tests.