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I Seriously Question The Accuracy Of The Libre Sensor.

Discussion in 'Type 2 Diabetes' started by Gork, Jul 8, 2018.

  1. Gork

    Gork Type 2 · Well-Known Member

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    My upper readings (150+) are a bit higher than when I use a separate test meter as a comparison but my Libre lower readings (120-) are seriously questionable. Just this morning, my Libre gave a reading of 81 while my Breeze2 test was 140. Had I relied on Libre, then I would not have taken the insulin. I will be documenting this sensor's readings even if I have to pay for test sticks myself.

    This is not a fluke in sensors or locations for the sensors. I questioned readings in the past but have never put them to the test. I will now document this. I plan to continue my discussion with the people at Libre and will strongly suggest that they at least supply me with free test strips. I will tolerate the finger sticks because I want to know which system is accurate.

    I am inclined to believe that my original Breeze2 test strips were accurate because my numbers matched those needed for very good A1c test results. However, time will tell.

    Please let me know if you have seen anything similar to this with your sensors, Libre or not.
     
  2. Deleted Account

    Deleted Account · Guest

    I found the Libre (and Dexcom) very inaccurate with no logic to the amount or direction and just concluded I was incompatible.
    This maybe because I move a lot which wiggles the sensor around (so it never settles down) or because my BG changes quickly (so the 15 minute delay is significant).
     
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  3. Scott-C

    Scott-C Type 1 · Well-Known Member

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    @Gork , according to my reader stats, I'm now on my 57th sensor, been using it for about 2 years now.

    Sure, 4 or 5 of those sensors have been plain sketchy and untrustworthy, Abbott have been ok with replacing them.

    I'd urge you not to jump to conclusions too quickly about them. It can take a few months to figure out libre's quirks and foibles.

    I think that new users are sometimes frustrated about the differences between a libre scan and a bg test. But, behind the scenes, there's sometimes perfectly legitimate reasons for those differences.

    For example, you say that in the morning libre read 81 and a bg test read 140. Obviously, I don't know the full context in which that happened, but something I'd offer as a general observation from my own experience is that on getting up in the morning, I get a subset of "dawn phenomenon" called "foot on floor" - I'll easily go from 5 to 9 just by getting up as my body prepares itself for the day ahead. I deal with it by a 2 or 3u pin.

    How that relates to libre questionable results is that the glucose is released into the bloodstream first and it takes time to then be distributed around the body and seep out through capillaries into the interstitial fluid, which is what libre is measuring, not blood directly.

    So, let's say you've got a bit of "foot on floor" going on. It's entirely possible that glucose in blood is x and glucose in interstitial fluid is y, and y is substantially less than x because the glucose in blood hasn't yet got to the interstitial fluid.

    Another example would be when I'm trying to correct a high of, say, 8 or 9. I'll inject a few units, and then watch despondently as the libre seems to show no drop to 5 happy land. But then I'll do a bg test and I'm at 6. So the 2u has worked, libre is still showing 9, meter is showing 6, big difference, but it's entirely explainable because changes in bg take time to show up in IF. It's why we need to not just look at the number - we need to think also about what else is going on. In this example, there's active IOB hitting hard, and it's dropping in blood first, and will take time to be reflected in IF later, so I would expect libre and bg to differ.

    I think that many new users fail to appreciate the time aspect of this, caused by the fact that bg and IF are different things.

    BG, even in non-Ts, isn't actually that stable. It's a constantly moving dynamic system with inputs and outputs, so there's bound to be situations where glucose in blood and in IF differ - for biological reasons, not sensor error.

    I was just as frustrated as you are in my first couple of weeks with libre. But I persevered, and after a while it becomes easier to read it. I think many make the mistake of just looking at the number without factoring in the surrounding context, the differences between blood and IF, and failing to consider that time makes a difference.

    To make sense of it, it's important to take into account the biology of the relationship between the blood and IF spaces, cross-check against last bg test and where you might expect to be based on last bolus/carbs.

    There's third party add-ons such as blucon from Ambrosia Systems and MiaoMiao from High Brilliant Technology, which let you calibrate output from libre. They're small transmitters which are placed on top of libre and ping readings to your phone every 5 mins.You type in a bg reading so that the programme knows that the x it's getting from the sensor means x in terms of bg. My blucon, with an android app xdrip+ has tidied up a few sensors which I would have otherwise have sent back. MiaoMiao is good for iphones as it runs through an ios app, Spike. Plus they do high and low alerts, which makes life on insulin soooo much easier.

    But, of course, there are some people for whom these things just don't work at all. I don't know the exact reasons why, but you're basically putting something into your body which isn't meant to be there, so the "foreign body response" kicks in to try to repel it, and even after that's given up the fight against a filament way bigger than they are, it can get clagged up with "biofouling", biological detritus swimming around in the IF, so that glucose can't actually get to the filament to be measured, hence fake lows. I'm not a doc or scientist, but it just seems that some people have biology which just makes them more prone to 'clagging up" sensors than others.

    Hope it works out for you eventually, but it can take a bit of time getting used to it.
     
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  4. ThePenguinPimp

    ThePenguinPimp Type 1 · Well-Known Member

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    Are you rising or falling when you test? I've been on a cgm for 12 years and I know if I test when I'm rising or falling quickly it's likely to end up with an inaccurate cgm reading later on due to the time delay between my blood reading and the layer where the sensor takes its reading.

    I watched a youtube review of the dexcom g6 sensor and was put off totally as they said it took a day before it settled down and was anywhere close to the actual reading (I could not be doing with this once every however many days you change it).. however this was just one review and I have no desire to change to it anyway lol.
     
  5. Gork

    Gork Type 2 · Well-Known Member

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    I just went through 4 days (5 - 6 readings a day) and all of them were 40% to 120% lower than my Breeze2 test strips showed. Some readings just said LO while others told me to check back in 10 minutes. A new sensor is within the "20% acceptable range". That is right, the Libre system is generally off by 20% and that is acceptable by Libre.

    If I did not question the results that the sensor was giving and relied on the readings then I would not have been taking enough insulin and my A1c would have been rising. It would have been another two to three month before I knew that the damage was happening.

    I had a long conversation with Libre and they are sending a new sensor. They refuse to send me test strips so that I can verify their sensors. Really, there should be at least enough test strips to cover the 12 hour delay with a new sensor.

    This is all so very unfortunate because I really like the system (otherwise). Not only will I be able to stop the five finger sticks a day when I have a working set up but I get to show off my Borg implant.
     
  6. tom58

    tom58 Type 1 · Well-Known Member

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    I always use a Libre blood test strip if I'm in doubt about the Freestyle Libre meter reading. Happily Libre strips are prescribed FOC by my consultant as a backup and also as a verification. I live in France so the rules of the road are not the same but I understood that you had to take a blood test rather than a meter reading before you got behind the wheel in the UK. Surely strips are therefore available on the NHS if they give you a meter.
     
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