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What's acceptable in glucose meter descrepensies

Discussion in 'Type 1 Diabetes' started by DannyH, May 7, 2022.

  1. DannyH

    DannyH Type 1 · Well-Known Member

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    Hi again, just wondering what is acceptable in glucose meter readings and libre sensor. Below is a few pictures taken shortly after one another on different days and compare results, it's pure hit and miss. I've tried changing the batteries etc. But trying to control my diabetes better but need the data to be accurate. I know the readings are rubbish and either readings but these were taken a few minutes apart, one example is is I did a scan on libre said it was around 18 then to double check I checked my sugars on a meter about 10 or 15 minutes later said is was 11.6 thought that was crashing way fast to what insulin I've had so then I check sugars again on meter and said 17.5 so I went with around that, unsure what's more accurate the libre or meter, and as I had a reading of around 18 on both the libre and meter and went with that and ignored the 11.6, but I am finding iam scanning on libre then a couple of meter tests and what comes back in the similar ball park I usually go with that, iam on a 4sure meter has anyone had issues with them, IL ask when I see the specialist next week, but struggling to do the right amounts of insulin if the readings are different all the time. I know the the higher the sugars the more it can be out.
     

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  2. Marie 2

    Marie 2 LADA · Well-Known Member

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    A meter is definitely more accurate. Although any meter can go whacky. And some meters are more accurate than others.

    It would have been nicer to have been at the 11 than the 17! So the meter said an 11.6 and then an 17.5? Had you had any simple sugar within 15 minutes or so before or during those readings? Because your blood sugars can change fast from that. But you need to judge when your insulin was supposed to hit, any food hitting etc. If none of that, you might need a new meter.

    You do have to allow for an amount of discrepancy. A lot of us acquire more than one meter so that if there is a question you can compare the readings on the two to see if they are close, they usually will never be exactly the same. I know several people like me when we get a blood test we will do a meter read at the same time to find out how accurate our meter is.

    But a sensor is a whole different thing. First it reads interstitial fluid, not blood and there is a delay of anywhere between 10-20 minutes versus a meter which is off of a blood sample. On top of that a Libre sensor is notoriously off, it usually reads lower, anywhere from .3mmol-1.mmol lower on me. But the trick is, it will tell you what you are trending, so you can tell if you are trending steady, dropping, or going higher. It will give you an idea at any given time what your BG level is doing. The idea being even if inaccurate if you are at 11 or 17 or 24, you are too high??? But in any critical decision a meter is best to use.

    And yes at higher numbers the sensor will be more inaccurate.They usually tell you to allow for a 20% inaccuracy. If it stays off for no reason you can call Abbot/Libre and they will replace it.
     
    #2 Marie 2, May 7, 2022 at 9:56 PM
    Last edited: May 8, 2022
  3. EllieM

    EllieM Type 1 · Moderator
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    Meters are supposed to be accurate to within +-15%
    https://www.diabetesqld.org.au/news/how-accurate-is-your-blood-glucose-meter/
    In meters, readings greater than 4.2 mmol/l, must have an accuracy of +-15 per cent for 99 per cent of readings.

    But they can also be off if there are contaminants on your hands. I use a dexcom and find it can be pretty inaccurate at the beginning and (sometimes only) end of a sensor life. If in doubt I make sure my hands are clean and do a second blood test, also remembering that the interstitial reading lags slightly behind the fingerprick (relevant in times when readings are changing rapidly).
     
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  4. Yaya10_10

    Yaya10_10 Type 1 · Well-Known Member

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  5. Bittern

    Bittern Type 2 · Well-Known Member

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    As said above meters have an accuracy tolerance of +/-15%, what this means in practice is a reading of 10 may actually be 11.5 or 8.7 or anything in-between. So a reading of 17 could be 19.6 or 14.7 or anything in between.

    The first problem you have comparing meters and Libra is that the Libra also has a an accuracy tolerance, say +/-15%, I don't have the actual figure to hand, so if your meter is at the lower end of its tolerance, say -15%, and the Libra is at the higher end of its tolerance +15%, the difference in readings could be 30% which is still within the manufactured allowed tolerances, ie the meter can read 11.5 Libra reads 8.7.

    The second problem is that blood glucose can vary very rapidly so readings taken seconds apart can be different. even using the same meter.

    The third problem is that a meter and a Libra do not measure the same thing. The meter reads, fairly directly, the level of glucose in the blood and the Libra reads the level of glucose in the fluids between the cells at the site of the Libra and then corrects that number to blood glucose using a built in algorithm.

    The fourth problem is that the glucose level in your blood, read by a meter, will vary much faster than the interstitial glucose readings taken with a Libra, thats just the way your body works. So the Libra reading is likely to lag the meter reading.

    My advice for what it's worth is find a meter that you like or the NHS will give you and stick to it, using the Libra readings to look for trends in levels over time.

    Sorry for the long post but I hope it explains things a bit.
     
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    #5 Bittern, May 8, 2022 at 9:11 AM
    Last edited: May 8, 2022
  6. StewM

    StewM Type 1 · Well-Known Member

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    I'd say washing and drying your hands properly is a major one. I've seen differences of more than 15mmol/l, when I've had contaminants on my hands, and false lows if my hands are still even a little wet.
     
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    • Informative Informative x 1
  7. StewM

    StewM Type 1 · Well-Known Member

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    Just to add to your excellent post. Libre has a tolerance of +/- 20%.

    However, Abbott also say the tolerance is even higher;
    1) during the first 24 hours of a sensor,
    2) during and 15 minutes after physical activity.
    3) at extreme Blood Sugar levels (<3.0 and >13.9mmol/l).
     
    • Informative Informative x 3
  8. Oldvatr

    Oldvatr Type 2 · Expert

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    Just to add that when comparing two meters even on the same drop of blood, one may read 15% high and the other 15% low, giving a difference of 30% where neither meter is giving a 'wrong' reading.
     
  9. HSSS

    HSSS Type 2 · Expert

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    And I rarely get the same reading from the same meter on the same blood drop either! Up to a mmol out failry often.
     
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