Vast differences between meter and lab

[Protimenow]

I feel as if I've almost hijacked a thread, reporting on my experiences with an anticoagulation lab, and experiences with my meter(s), and a minor (thank god) stroke.

I thought I'd move some of this stuff to a new thread.

A few things:

Right after I felt the symptoms of having a stroke (I suspected that it might be a stroke vs. my leg falling asleep and taking a while to wake up), and after taking two aspirin, I checked my INR. The meter told me I had an INR of 2.6 -- too high to put me at risk.

A day and a half later, the hospital lab got a 1.7. It seemed to be too big a drop in that short a time, and made me suspect that the meter was reporting values that were higher than actual. I thought that with a low battery (I didn't realize it was so low until I tried to copy results off of it), and a five year old meter, PERHAPS the meter was reporting values that were higher than actual, and that as a result, my INR was below 2.0 for an extended period of time.

Alere sent me a new meter and some new strips. I put new batteries into both meters. My INR at the Anticoagulation lab (which I probably can do quite well without), on 4/25, was 2.5 - right where they wanted it. On 4/26, the InRatio 2 got a 2.4 -- within where I kind of expected it to be. The next day, using the InRatio - I got a 2.8 -- a bit higher than it should have been (maybe) only 14 hours after the InRatio 2 result, but acceptable.

On Tuesday - within about two minutes of each other - my InRatio and InRatio 2 both reported 3.8. This result seemed pretty credible and reliable - a bit high, but okay.

My surprise came a few minutes ago when I finally got the results from the blood draw that was taken about 90 minutes after my InRatio tests -- 3.09. This was done at a hospital lab. This result makes me wonder if the hospital lab may not be using the right thrombin reagent, or isn't calculating the INR properly, or something. The hospital lab results have been consistently below InRatio results -- and by about .7. I'm inclined to question the hospital lab, rather than the InRatio meters. (FWIW - the Anticoagulation Clinic's ITC meter reported values that were close to the InRatio meters).

As I mentioned, I feel like I've partially taken over the 'Truth' thread, and thought that it may make sense to start a new thread about this.

So -- do I contact the lab or the clinic and question their procedures so that they can check to validate their results? Do I contact the clinic and suggest that they compare their meter to the lab results? Do I do nothing, and wait for my next fingerstick at the Clinic on Tuesday and compare it to my meter results? Certainly, if the lab is reporting INRs lower than actual values, there may not be a problem until they get patients with INRs at the high end of their range (and thus, perhaps, at risk of hemorrhaging), but for others, shooting a bit high may not be a major issue.

What do YOU suggest that I do?

 

[newmitral]

With a single individual and only a few tests that don't agree, each test entity will likely just point the finger at the other.

However, if we can get a significant number of statistics that points to a systematic bias when comparing venipuncture Lab INR readings to home-meter INR readings, then we will be in a much stronger position to get real answers, even if such statistics gathering is not a completely rigorous scientific study. From my (admittedly limited) research into the question, it seems that the lab tests are the "gold-standard", and the meter accuracy claims are tied to comparison with those results for validation.

This forum provides a unique opportunity to quickly collect a lot more data points from a large number of home INR testers, where we can get comparisons of venipuncture versus meter results from a lot of members.

Perhaps starting a quasi-poll type of thread, much like the tissue-versus-mechanical thread in the valve selection area of the forum would be useful.

If we get a few hundred data points over time, we might be able to draw some real defensible conclusions. We might be able to determine that one type of meter is more consistently in agreement with lab results than another.
If a consistent trend of inaccuracy at higher meter readings is confirmed from many users and many tests, then the meter manufacturers are likely to take user concerns more seriously. Conversely, we might find that the occasional statistical outlier is just par for the course, and the bulk of the test results are fine.

Below are typical data/questions that might be useful, with info from my single INR comparison :

1. Date of test
Answer: 11/23/2011

2. Time Between Meter and Venipuncture Blood Draw
Answer: <90 minutes

3. Type/Brand of Meter:
Answer: Inratio2

4. Meter INR reading
Answer: 3.4

5. Blood Draw (not another meter) INR reading
Answer: 2.8

6. Complicating Factors (Lovenox Bridging, Lupus, Anemia, etc.)
Answer : None


I don't want to hijack this thread for such a poll, but would like to get your thoughts on whether you think it would be a useful thing to do or not.
If so, what additional data should be collected to make the study more useful?

Unfortunately, I can't offer any other suggestion as to how to proceed with your test findings as they are.

 

[Protimenow]

Some sort of poll may be of interest -- but my suspicion is that there may be something that is not being done correctly at THIS PARTICULAR LAB. I may be able to convince the clinic to let me get BOTH a blood draw and a finger-stick using their machine, then comparing the results. They may be obstinate, and tell me that they get their meter 'calibrated' every six months, and claim that it would be a waste of resources to run duplicate tests. Further, if it IS possible to calibrate their meter, the meter may be calibrated to possibly incorrect lab results. The real test may be blood draws within minutes of each other by two or more DIFFERENT labs. Of course, this can involve a fair amount of money, and a person's willingness to have multiple blood draws -- but it may reveal results that can impact the anticoagulation management of many people.

If I could find someone in my area who has a meter -- InRatio, CoaguChek XS, or even some current ProTime cuvettes, I would be happy to make comparisons between these devices. At this point, I neither have resources for multiple tests nor the prescriptions that I would need for a blood draw.

And, FWIW, research on the meter manufacturers' sites shows a pretty high level of agreement between blood draws and meter results.

The variability between labs is something that may not have been adequately studied.

 

[Protimenow]

This has really moved to another thread that I just started.

I may have been to quick to not trust the lab. In fact, Alere (makers of the InRatio) told me to TRUST THE LAB. My other thread calls into question an OTC that may have 'fooled' the meter into reporting INRs higher than they actually were.

As far as a 'poll' of meter-reported values and lab values -- such data may already exist, but would probably be impossible to get to because of patient privacy laws. (It would be great if some of our members - who probably should be logging their INRs anyway, could provide us with meter and lab INRs - but I suspect that few will be doing these tests in parallel.)


On Tuesday, I plan to have my INR tested with a different meter (from ITC) and compare it to my InRatio. It'll be a week since a blood draw, so no valid comparison to the meter results would be possible.