Meter Reading Variations

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Mountain Path

Mountain Path

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Relationship to Diabetes
Type 2
Not sure this is the correct forum to post this but ...

I have a Dexcom 1 at present and it seems to reading high and thus I think I need to take action (exercise) when perhaps I don't.

So I did a finger prick test and ....

Dexcom One : 8.3
Accucheck : 6.7
Safe AQ : 6.4
Contour :124 converts to 6.9
The last three used the same blood sample. No food today as yet.,

This is actually better then an earlier one where
Dexcom was reading 8.5, Accucheck 7.2 and Safeaq 6.2

In this case Dexcom would indicate some exercise biking may by required and SafeAQ would say relax and do some work.

Do others also get this sort of wide range, is there some standard way of calibrating these devices so they match or do I just pick a device I like and keep with it? (or perhaps a reading I like?)
 
Glucose meters have a 15% error margin from a lab result. (Less than that if the actual glucose level is < 5.6mmol/l)
Some are more accurate (Contour meters claim to be very accurate, I've seen figures showing that they are generally well within 15%, and usually lower than 10%.)
CGMs are not as accurate as blood meters, and during their lifetime the accuracy seems to vary.
6.7/6.4/6.9 are pretty much the same.
If you took a reading on another finger with, say, the Contour, you might get 6.4.

I tend to ignore the decimal point.
 
As @harbottle says, the meter readings are all basically the same. The Dexcom One reading higher is an issue. Always fingerprick if you’re about to do something based on a CGM/FlashGM reading as they can be inaccurate sometimes.

Are you on any medication?
 
Speaking strictly technically, I doubt whether those readings could be shown to be statistically significantly different.

My observations suggest that the number after the decimal point can be ignored, you simply cannot measure blood glucose with these devices to a reproducibility that would give that degree of precision. Note, I am deliberately not using the word "accuracy" in this context, that's a whole different ball game.

So, the dexcom gives you 8, the accucheck 7 and the safeaq 6. Since each of those would have an error of at least +/- 1 and probably a lot more, all three are best considered to be the same.

@harbottle correctly points out that meters allow +/- 15% variability against a reference and I suspect that they are generally much better than that. What is not allowed for is sample variability which I suspect is much higher.

I'll throw in my usual caveat that I am not knocking the kit, far from it. I think it is amazing that it can get anywhere near giving a sensible blood glucose reading. All I suggest is that you do not get too hung up on the numbers and try and read things into what are insignificant differences between different devices. Differences of 3 or more might be worth thinking about, anything less than that are best treated as part of lifes rich pattern.

If I were in charge I would ban the decimal point display on blood glucose meters and then insist on an error bar on the whole number.
 
Currently I am attempting to manage things by using a GSM, a no sugar and carbohydrate diet and exercising vigorously to mitigate highs (don't really get lows).

I was on 4 Metformin and 2 Glucacide per day, but managed to reduce this to zero apart from emergencies (mainly accidentally or purposefully eating something on the banned list.)

My doctor cancelled all my medication after the last review due to my reduced HbA1c and stated method, currently debating that I need an emergency backup as sometimes just cant exercise, but there is an issue with NICE guidelines apparently on this method (another thread here was about that).

The accuracy of my GSM is paramount to my methodology as exercise is time consuming and there is a limit to how much I can do, so its a bit annoying when it seems so far out.

Thanks to @harbottle and you for the useful feedback on overall reading accuracy.
 
If I were in charge I would ban the decimal point display on blood glucose meters and then insist on an error bar on the whole number.

I wouldn’t do that. I find I learn the funny ways of each meter and whether it reads higher or lower than my other meter. They become part of my decision-making kit, and I want to see whether my meter is saying 4.1 or 4.9. Perhaps it doesn’t matter for Type 2s not on glucose-lowering meds, but as a Type 1 I do take note of the decimal point. My pump likes that reading too. Once I’m familiar with a good quality meter and trust it, so to speak, it’s readings help guide me in the many decisions I have to make, along with my own experience.
 
Mountain Path said:
Currently I am attempting to manage things by using a GSM, a no sugar and carbohydrate diet and exercising vigorously to mitigate highs (don't really get lows).

I was on 4 Metformin and 2 Glucacide per day, but managed to reduce this to zero apart from emergencies (mainly accidentally or purposefully eating something on the banned list.)

My doctor cancelled all my medication after the last review due to my reduced HbA1c and stated method, currently debating that I need an emergency backup as sometimes just cant exercise, but there is an issue with NICE guidelines apparently on this method (another thread here was about that).

The accuracy of my GSM is paramount to my methodology as exercise is time consuming and there is a limit to how much I can do, so its a bit annoying when it seems so far out.

Thanks to @harbottle and you for the useful feedback on overall reading accuracy.
Click to expand...

If you want accuracy, you’d be better off using a meter. If you want the graphs, then a CGM or FlashGM is useful. But if you’re exercising to get down highs (good idea) then I’d fingerprick personally.
 
Yes, it is normal for there to be a significant error margin than the decimal place in the readings lulls you into believing.
The sensors are reading interstitial fluid rather than blood and they have an inbuilt algorithm to try to convert that to a blood reading but as individual bodies vary, it may be more accurate for some people than others. It may also be that the location you have the sensor placed is part of the discrepancy with the Dexcom. For instance I believe there was some discussion a while ago about some people finding that their right hand gives slightly lower readings than their left hand with BG meters and this may be down to the physiology of their dominant hand/arm being very slightly different.... glucose absorption/insulin sensitivity being slightly better in the dominant arm.

For me using the orginal Libre sensors, they are pretty consistently about 1mmol lower than a finger prick reading (using a Caresens Duo meter) I automatically factor this discrepancy into my calculations for insulin or carbs but I always do a couple of checks on the first day of each sensor and another few randomly throughout the lifespan of the sensor just to make sure it hasn't drifted. Mostly I find they stay pretty consistent. Occasionally I have had a sensor which has been up to 2mmols lower which is a pain but I can manage it and I keep a closer check on those. Consistently more than 2 mmols out is unacceptable for me and I report them, but it happens very rarely. Of course, I have no way of knowing how close my Caresens readings are compared to actual BG other than that they normally correspond pretty well to when I feel hypo and of course they are supposed to be within 15%.

I am not sure if you can calibrate the Dexcom (you can't calibrate Libre) but I think in your situation, if I tested a few times when my levels were stable and the Dexcom was reading about 1.5 mmols higher i would just factor that into my thinking when I needed to make decisions regarding taking action like exercise and stick with whichever BG meter I had most confidence in for double checking it.... or calibrating if the Dexcom does actually have that option.
 
Docb said:
Speaking strictly technically, I doubt whether those readings could be shown to be statistically significantly different.

My observations suggest that the number after the decimal point can be ignored, you simply cannot measure blood glucose with these devices to a reproducibility that would give that degree of precision. Note, I am deliberately not using the word "accuracy" in this context, that's a whole different ball game.

So, the dexcom gives you 8, the accucheck 7 and the safeaq 6. Since each of those would have an error of at least +/- 1 and probably a lot more, all three are best considered to be the same.

@harbottle correctly points out that meters allow +/- 15% variability against a reference and I suspect that they are generally much better than that. What is not allowed for is sample variability which I suspect is much higher.

I'll throw in my usual caveat that I am not knocking the kit, far from it. I think it is amazing that it can get anywhere near giving a sensible blood glucose reading. All I suggest is that you do not get too hung up on the numbers and try and read things into what are insignificant differences between different devices. Differences of 3 or more might be worth thinking about, anything less than that are best treated as part of lifes rich pattern.

If I were in charge I would ban the decimal point display on blood glucose meters and then insist on an error bar on the whole number.
Click to expand...
Thanks Docb,

I guess I want to stay within recommended ranges which are, I understand max 7 Pre Prandial and max 8.5 post Prandial. Ideally staying 4-7 all the time. With an error of +/- 1 then that would be 8 and 9.5.

I will set my high alarm for 10 and do multiple checks when they go off.

Pity there is no absolute device that can be used.
 
Inka said:
If I were in charge I would ban the decimal point display on blood glucose meters and then insist on an error bar on the whole number.

I wouldn’t do that. I find I learn the funny ways of each meter and whether it reads higher or lower than my other meter. They become part of my decision-making kit, and I want to see whether my meter is saying 4.1 or 4.9. Perhaps it doesn’t matter for Type 2s not on glucose-lowering meds, but as a Type 1 I do take note of the decimal point. My pump likes that reading too. Once I’m familiar with a good quality meter and trust it, so to speak, it’s readings help guide me in the many decisions I have to make, along with my own experience.
Click to expand...
Apologies @Inka. Should have added my normal caveat that my comments on meter readings are best confined to T2's. T1 is an entirely different ball game.
 
harbottle said:
Glucose meters have a 15% error margin from a lab result. (Less than that if the actual glucose level is < 5.6mmol/l)
Some are more accurate (Contour meters claim to be very accurate, I've seen figures showing that they are generally well within 15%, and usually lower than 10%.)
CGMs are not as accurate as blood meters, and during their lifetime the accuracy seems to vary.
6.7/6.4/6.9 are pretty much the same.
If you took a reading on another finger with, say, the Contour, you might get 6.4.

I tend to ignore the decimal point.
Click to expand...

Not exactly.

ISO: Readings are 95 percent accurate within 15 percent of blood glucose equal to or above 100 mg/dl and are 95 percent accurate within 15 mg/dl for readings under 100 mg/dl

Sometimes they meet that.
But for 5% of the time they can read anything they want to.

And blood varies from finger to finger, heart rate, temperature, mostly anything really.
 
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