Find one test method and stay with it? Pshaw

[Protimenow]

I've been testing for many years, primarily using the Coag-Sense meter.
Years ago, I was testing with the Coag-Sense, CoaguChek XS, other meters, and a blood draw. I wanted to find the meter that most accurately echoed the lab results.
At that time, I chose the Coag-Sense because it often matched the lab results (for me, at least) and was sometimes .1 or .2 below the lab. I reasoned that I'd rather have my results lower than the lab so that I don't EVER have my INR fall below 2.

More recently, my Coag-Sense has differed from the labs ny as much as 2 points (not tenths of a point). Last week, I got some CoaguChek XS strips, and my difference was .9 and 1.2 points -- probably closer th the hospital lab than they were to the Coag-Sense.

Coagusense of course stood by the accuracy of their meter. I suspect that Roche and the labs will also stick by the accuracy of their methods.

Now, here's the thing:

I was told by a lab that I should find one method to evaluate my INR and stick with it. Trying to compare one meter to the other, and to the lab, can drive me nuts.

I was told the same thing by Coagusense - stick with one method.

While this sounds like good advice, there's a hold big enough to drive a truck through if using this logic:

If a person sticks with the lab, for example, and it gives a result of 4.9 (as my lab did when I was in the hospital), and my Coag-Sense was 3.0 the day before, if I stuck with the lab's reeporting that I was considerably above target range, I'd substantially reduce my dosage, and maybe even skip a day's dose. This ASSUMES that the lab is right.

OTOH - if I stick by my meter's 3.0, no changes would be necessary. Skipping a dose, and reducing my dosage could, conceivably, throw my INR into the 2s and maybe even lower.

Thus, the results of sticking to one est method will result in dosing changes that may not be healthy. Trusting one method over another that varies by 1 point or higher than the other method sounds to me like a recipe for disaster.

Any thoughts?

 

[tom in MO]

"A man with a watch knows what time it is. A man with two watches is never sure."

Each human is different, and blood chemistry can be complex. Maybe your blood chemistry is not amenable to drop testing by meters. The standard is blood draw testing. Maybe you should test once every two weeks by lab blood draw (no meters) and use only this value for dosing

 

[Protimenow]

You've missed my point.

Your quotes should be updated:

A person with a watch thinks he knows the time. That time can be way off the actual time. It's like a lab whise results are 1 point above the accurate INR to think that its results are accurate. Making dosing decisions based on that assumption can result in real danger.

A person with two watches is never sure. Again, this is wrong -- if this person had a quartz or more accurate watch, and synchronized it with an atomic clock (or even an application on the phone that is accurate), then that person would 'know the time' within a second or so each month. If you use a method for determining INR that you trust, then appropriate dosing decisions could be made.

I've been testing my INR for 11 years. I did a lot of comparison testing between lab, CoaguChek XS, Coag-Sense, and other meters for about a year. During that time, all three gave somewhat similar results, except for the XS which had a variance from lab and Coag-Sense that increased the higher the INR was.

For the last few years, I've found that the difference between my meter and the labs has increased. Im not sure why. The manufacturers of the Coag-Sense insist that they stand ny the accuracy of their results. I'm starting to do a three source comparison between Coag-Sense, CoaguChek XS (I would gladly accept donated strips to support this testing), and one or more labs. I'll run through at least four of each type of test strip each week (I may test more than once a week on each machine) and my goal is to get a blood draw monthly.

I'm not entirely sure of the accuracy of the labs. In any case, if I was to rely only on lab results, I would test weekly - not every two weeks.

My challenge is to determine differences between meters, and compared to the labs. Depending on which source I trust, I'll make dosing decisions. The real issue is 'which source I trust' - and I'm not convinced that it's the labs.

Then, too, I've also brought up the remote possibility that there is something about my blood that lab tests don't properly work with - but if the method of detecting a clot with my Coag-Sense and lab are similar enough, there should be minimal differences. (Unless the lab has stopped using the 'tilt table' method of detecting a clot, the results should be very similar to the Coag-Sense physical detection of a clot). If the labs have changed from the physical method of clot detection, differences may not be all that surprising.

 

[Protimenow]

Now it's getting interesting.

I'm comparing my INR readings from Coag-Sense and CoaguChek XS, and to occasional lab tests.

The CoaguChek XS reported INRs 0.8 and 1.1 higher than the Coag-Sense did last week.

Just now, the Coag-Sense gave me a reslut of 2.7 - and a few minutes later, the CoaguChek XS returned a 3.7. A few minutes later, in an attempt to get a bigger drop of blood, I tested again using my Coag-Sense, with a lancet positioned closer to the fingertip. I got a 2.8 - within any stardard of error against the early Coag-Sense result.

Both companies stand behind the accuracy of their results. I'll have to get a lab test, and almost simultaneously test using both meters, and perhaps I'll get a result that's closer to one or the other. I'm guessing that Roche will probably be closer to the labs than Coag-Sense.

I see my electrophysiologist on Thursday. I don't expect him to have a meter, but he may be able to give me a prescription for a blood draw.

In any case, I've started my comparative studies of the two meters. This continues to leave me wondering about whether there's a factor in my blood that a) makes the Coag-Sense method of detecting a clot inacurate or b) makes the CoaguChek XS and labs give a higher result. Or, perhaps, I've become something of an anomaly who can't be accurately tested using one method or another.

Which value do I use to manage my anticoagulation? If I reduce my dosage based on a 3.7, what will that do to my INR as reported by the Coag-Sense? According to my coag-sense meters, my INR is on target. Do I worry because the INR reported by the CoaguChek XS is a point higher? Here's where trusting only one test method can become an issue.

I'll do continued testing, as long as my XS strips hold out, and maybe decide which to trust.

 

[Eva]

“....and perhaps I'll get a result that's closer to one or the other..

I see my electrophysiologist on Thursday. I don't expect him to have a meter, but he may be able to give me a prescription for a blood draw.“

And stick to the one closer to the land. Forget the others. The difference in ratio between your machine and the lab will always be the same. So, you can adjust your warfarin accordingly. Good luck. The more machines, the more confusion, more stress, less attention to better results!

 

[Protimenow]

Yes, but Eve, how do you know which one is 'closer to the land'?

Years ago, when I was testing multiple machines against each other and against the labs, all three were pretty close to each other. This made it easy to choose one meter that I could trust. It's different today.

I don't want to be over-anticoagulated (although I'll take that risk) by modifying dosage from the lowest of the three, and I certainly do NOT want to be under-anticoagulated if I base dosing on the highest of the three (the lab). If I chose to trust the lab, I could theoretically wind up so under-anticoagulated that my INR may drop too close to 2.0 for comfort.

The question, in your terms, is 'where, really, IS the ground?'

 

[tom in MO]

You've missed my point....

You too have missed the point. INR is not an absolute, except for the blood draw. Just like time, there is no absolute for time other than the sun being at the highest point in the sky at noon, which changes with longitude...or is it latitude The standard for INR is blood draw, so if you really care to be "correct" that's the method for INR measurement that should satisfy you. If you use a different arm each time, you can easliy test every 2-weeks. Plus you'll only get one number, thus no confusion

 

[Protimenow]

True, INR is not a stable number, and testing INR is an art, not a science.
INR results are only as good as the labs. I've done tests at two different labs, within hours of each other, and gotten different results. I've had a lab completel botch INR testing for me and another of the doctor's patients -- and even with their running a second test on the same samples, still came up with results that were far different from those at two other labs.

If there was a reliable (I'm using 'reliable' as a statistical term, meaning that you'll get the same result each time you test something - in this case, all tests will be done with the same method, and appropriate settings if a new reagent is used) lab, perhaps I'd use it. BUT NOT EVERY TWO WEEKS. IT'll have to be weekly, for reasons that I've listed numerous times.

The meter manuacturers all stand by the accuracy of their results. As I mentioneed earlier, I'd rather be slightly overmedicated with Warfarin (meaning that my INR may wind up in the mid- to high 3s than undermedicated with Warfarin, potentially plunging my INR to 2 or below.

Sometimes it comes down to which method you trust the most. Sometimes, it's choosing the method with the potential of doing the least amount of damage.

In this case, I'd rather go with a test that gives me an INR of 2.7 (with the other meter showing a 3.7) than the meter with the higher number. This way, at least I'm comfortable that I won't have a stroke or pulmonary embolism by reducing my dosage.

 

[Agian]

Protime, you've probably already stated it, but what is your target range?

 

[ScribeWithALancet]

And stick to the one closer to the land. Forget the others. The difference in ratio between your machine and the lab will always be the same. So, you can adjust your warfarin accordingly. Good luck. The more machines, the more confusion, more stress, less attention to better results!

Eva,

You said "The difference in ratio between your machine and the lab will always be the same". Dr. Johnson, in tests at the University of Utah Medical School's AntiCoagulation clinic showed the exception(s) that prove the rule.

If the reagent used in the Lab machine or the INR test meter change, or if the machine used by the lab changes (or the lab sends excess work out to another lab that has a different machine) or if your machine changes, all previous ratios go out the window.

ProtimeNow mentioned another exception, your blood may chemically change over long periods of time. Periodically rechecking the ratio, as ProtimeNow is doing, and bugging the lab about what they are really doing is the only way to keep these exceptions under control. Unfortunately, some of us have health plans that switch which labs we are to use and this will likely break the ratios as well. Pellicle posted a study that shows that ISI calibrated labs can vary as much as 0.5. : - (

ProtimeNows approach of picking the set that shows he is in range on the low side and barely out of range on the high side is probably safest to avoid a stroke. The chart that Pellicle posted with the U shape risk curve for low and high values makes this the lowest risk approach. Unfortunately, it is lowest risk not no risk. We are not walking a tightrope but are walking on a narrow path. There is a medical term for it but I cannot recall it just now.

Walk in His Peace,
Scribe With a Lancet

 

[Protimenow]

Agian: I didn't mention my target in this thread. Before I got my stent, and started taking Plavix, it was around 2-3.5. I have a now fairly old (28 years) Aortic valve. Post-stent, and now with Plavix added, my cardiologist wants 2.0 - 3.0. My current feeling about which method to trust - or at least, to choose, keeps me with my Coag-Sense, with a target range o 2.0 - 3.0. Even if the CoaguChek XS (and maybe the labs) report 1.0 higher, my INR would still be in 3.0 to 4.0 - which I'm not particularly uncomfortable about.

 

[Sheenas7]

I just started home testing with Coagu Vantus System using Coagu check XS strips. My results are 3.0.
My target range for mechanical heart valve for mitral valve is 2.5-3.5.
So what is a value of 3.0 then? That I assumed was ideal. Isn't it?

 

[Protimenow]

A value of 3.0 IS ideal. It puts your INR (according to your meter) smack dab betweem 2.5 and 3.5. Measuring INR isn't a science - if you repeat the test, it may give you a slightly different number, but probably not one to be concerned with (maybe a 2.8 or 2.9 or 3.1 or 3.2). THe range is the target - anywhere within the range should be fine.

 

[tom in MO]

Measuring an INR is "science;" pretty sophisticated science really. Just not easy to understand since it's not a direct measurement but a normalized ratio.

 

[Protimenow]

I guess you can call just about anything science. Even with the best labs, with the most accurately adjusted reagents and equipment, you will probably be unable to get the same results of tests of blood from the same collection and the same tube of blood. If you check the literature, you'll see it referred to as inexact -- the nature of testing INR IS subject to inaccuracies - which makes this an art, not a science.

There's wiggle room for any of the diagnostic methods for testing prothrombin times - INR is simply the prothrombin time divided by a value for the reagent. (And the reagent values aren't always accurate).

 

[Sheenas7]

A value of 3.0 IS ideal. It puts your INR (according to your meter) smack dab betweem 2.5 and 3.5. Measuring INR isn't a science - if you repeat the test, it may give you a slightly different number, but probably not one to be concerned with (maybe a 2.8 or 2.9 or 3.1 or 3.2). THe range is the target - anywhere within the range should be fine.

Today was my day to test. I always wonder if I am doing it right. So I did it twice. 3.3 the first and 3.4 the second. Last time I was 3.1. So I took Tylenol this week for a bad back and also the days I felt terrible my diet changed. I had no wine with my dinner. So looks like I didn’t change too much. At most I have one or two wines. It reassured me to do it twice but I guess that’s 2 strips instead of one. I was told after I report 8 times they send me more strips.

 

[tom in MO]

I guess you can call just about anything science. Even with the best labs, with the most accurately adjusted reagents and equipment, you will probably be unable to get the same results of tests of blood from the same collection and the same tube of blood. If you check the literature, you'll see it referred to as inexact -- the nature of testing INR IS subject to inaccuracies - which makes this an art, not a science.

There's wiggle room for any of the diagnostic methods for testing prothrombin times - INR is simply the prothrombin time divided by a value for the reagent. (And the reagent values aren't always accurate).

INR testing is not art. That's nonsense.

Millions have their INR tested all over the world and receive treatment w/o difficulty. That's not art. You're experience is just an outlier. Having outliers is science too

 

[Protimenow]

Lets ask others what THEY think.

Your ridiculous argument that because 'millions have their INR tested all over the world and receive treatment w/o difficulty' doesn't account for the fact that these dosage recommendations are based on an inherently inaccurate measurement. Your argument implies that dosing is based on exact values -- and it isn't. The WHO says that INRs within 20% of a given value are acceptable -- with 'wiggle room' of 20%, how can you argue that this is science?

Pellicle and others - what do you think? IS INR testing art or science?

 

[Protimenow]

Sheenas7 - other than taking antibiotics or eating a lot of dark greens that you don't normally take, or getting a dose of Vitamin K1 (this may be hard to spot in multivitamins - the listing is usually pretty small), your INR probably won't change much. It seems like you're doing the testing exacly the way you should be. Having a difference of .1 or .2 from test to test - even if taken a few minutes apart, is normal.

Also, sometimes wasting a strip, or testing twice if you aren't sure about the results of the first, should be accepted by your strip provider.

 

[pellicle]

Any thoughts?

The flaws in your theory are:

• that a lab is seldom as consistent a pharmaceutical like Roche, so once you know that your blood is not the type that falls into the ~2% of the population who can't use these tools then use it.
• you focus on the numbers not the intention to treat. Its not the INR per se that's importat its the balance between reduction in thrombosis and bleed control. We know that the safe zone in AC therapy is wide, so its actually an easy target to maintain

So pick one and just stick with it unless evidence emerges not to. Which is essentially what you have done with your Coagsense. I know your TIA events spooked you for a bit, but I think that your response of obsessing about the INR number was not the most fruitful.

Somethings can be overcomplicated by over analysis.