INR +0.2 in 6 hours ...

[realkarl]

I measured 1.72 on my INRatio2 at 8am this morning, and when I went to the lab and drew blood for another test at 2.20pm, it was 1.9.

Either I am a little disappointed in the accuracy of the INRatio2, or I am surprised the INR can go up 0.2 in six hours for no apparent reason.

Thoughts?

Another question: I set my INRatio2 to display both ProTime and INR. It appears its calculation of INR from ProTime is a division by 10. However, the numbers from my lab was PT = 22.4 and INR = 1.9.. I guess the INRatio2 ProTime number is a different measure than the lab's, and I should have set the device to display INR only - so it would not create unnecessary questions

 

[Cris N]

To be honest this is meaningless. You could have a bigger difference if you tested a minute apart using the same equipment. In reality INR can vary throughout the day - sometimes it just makes a difference on which capillary you hit.

Also, what makes you think the lab test was correct?

INR is never a precise measurement - it's constantly fluctuating - that's why you have a range rather than a set number - and the range should be big enough to hit most of the time - lest you go crazy!

In time you will learn to trust your meter... Oh, forget the protime reading - the only one that makes any sense is INR. The protime number is so dependent on the reagent used - if you try to compare it to the lab's it's like comparing apples & oranges.

 

[realkarl]

Good to know, Cris. Thanks!

 

[dick0236]

INR is never a precise measurement - it's constantly fluctuating - that's why you have a range rather than a set number - and the range should be big enough to hit most of the time - lest you go crazy!

.

Chris is "spot on". New people to warfarin place way to much importance on minor changes in INR. It truly is not very complicated, or precise. Any number inside your given range is a good reading......and you will become comfortable with ANY number withing your range after you are on this stuff for awhile.

 

[Blanche]

I certainly agree with Cris N

I certainly agree with Cris N

Karl:
What you need to do is to make yourself an expert in Anticoagulation, International Normalized Ratio (INR), home testing, and other relevant information having to do with your anticoagulation treatment.

My husband has been home testing since we found this site in March 2001....and we still find information and research that we did not know about before. It may not be brain surgery, but knowing the "facts" about anticoag and all that goes with it is most important and I would say vital. You have only been doing this for less than a month.

This site certainly contains a wealth of information and a large number of folks who have become very experienced in anticoag...but you need more...IMO.

THis is what I suggest. Start right here on the board for "Reference Sources." THen, Choose "Must have reference links." Check out topics that deal with INR, Anticoagulation, etc. Once you become familiar with the topics, branch out and do some searches on the net. THere is a ton of good information available.

And most importantly, check out the site for Al Lodwick, who was an anticoagulation provider for years and is a member of this valvereplacement.
see: www.warfarinfo.com

It's like buying a car or a washing machine...you would not take it out for a spin without reading the user's manual first.

If I can help, let me know.

Kindest regards,
Blanche

 

[realkarl]

Yes, I have been reading most of the material, but as shown here, there's always more to learn. I had been spoiled by having a near constant INR for 2 months

 

[Bina]

Yes Karl, the INR will fluctuate a bit on its own. You are doing just fine.

 

[lance]

Hello Karl,
You're just experiencing warfarin being warfarin. All is well. There is an acceptable .8 difference allowed between my XS and the lab result. Do you know if this is true for your monitor?

 

[Ross]

With the INRatio, up to .6 variation.

 

[HemosenseTech]

If you all would like complete clarification on allowable variance I can list it for you. W.H.O (World Health Organization) has standards for INR comparisons when testing two different methods, primarily a POC (Point-of-Care) device compared to a reference method (lab). W.H.O is who tells the manufacture if they're compliant or not, along with the F.D.A. W.H.O. has 3 different "allowable" ranges that any P.O.C monitor has to fall within.

0.0-2.0 - 90% of POC systems results must be within +/- 0.5 INR units
2.0-4.5 - 90% of POC systems results must be within +/- 30% of reference method
>4.5 - No correlation criteria for results above 4.5 on the reference method.

I hope this clears things up for the future.

 

[lance]

This raises a few questions

This raises a few questions

HSTech

You have raised more than a few questions.
Over 4 years in use my "S" and "XS" when tested against the lab their accuracy has been 100% within the guidelines set down by the manufacturer. The worst discrepancy occurred recently when the lab test was sent out of town for processing and that was within the guidelines.
I don't understand the 2.0-4,5 explanation. What does the 30% refer to?
I think expecting 90% accuracy is next to useless when INR is concerned.
I've often wondered why medical personnel feel monitors are too inaccurate and won't use them maybe that's why.
I trust my monitor over any lab.
FDA and WHO standards are too low.

 

[HemosenseTech]

The way to think of this is like this: Hypothetically speaking you go to a lab and get a 3.0. When you test on any meter right away it needs to fall within 30% of that value. So 30% of 3.0 would be 0.9. So if you take the 3.0 you can go up or down by 0.9. So hypothetically speaking a meter could be as low as 2.1 and as high as a 3.9 and be "within" range. 9 out of 10 of your results in a comparison have to fall within this result range.

2 things to think about though. Meters generally do not fluctuate as long as your technique stays the same. This means that a meter would have a bias to the lab. So again, hypothetically speaking, say you testing and got a 3.0 in the lab, and a 3.3 on your meter. Let's say you did this 10 times or ran 10 different fingersticks against that lab. Chances are, if you technique stays the same, you're going to average out to a certain bias percentage to the lab. If you take the meter value (3.3) and subtract the lab value (3.0) and then divide by the lab value (3.0) you would get 0.10, multiple that by 100 (because it's a percentage) you would get a 10% bias. This generally means that anytime you test on your meter you are likely to get a 10% bias to the lab as long as your technique stays the same.

The second thing to think about is the difference in the way a lab and a meter tests (this is why the WHO and ISO has set ranges). There are generally 3 ways of testing INR. Optical (visual detection of clot), Mechanical (Having the clot physically move something), or Electrochemical (Electrical resistance when a clot forms). Amongst these 3 methods there are generally two sample types out there, whole blood, or serum. Amongst these 3 methods, 2 samples there are also different reagents used, each specific to the instrument (lab or meter). This gives dozens of possibilities as to an "exact" INR result, which would be different comparisons.

This really comes down to a which meter/which lab are you comparing. Chances are the results are going to be different, sometimes off by very little +/- 0.0 or 0.1 INR units. Sometimes this different can be large, up to 30% of the lab. The key here is that both INR results are correct, they're just different because of their methods, sample and reagents.

I really hope this helps. Here is a link to the document that breaks it down. The document is very technical so I tried to break it down so that actual numbers could be used for examples: http://www.hemosense.com/docs/5500330vC_TechBull109_ClinicalExpPT.pdf