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Freestyle Libre Sensor: highly inaccurate??

Discussion in 'Blood Glucose Monitoring' started by TedTomato, Mar 4, 2018.

  1. TedTomato

    TedTomato Prediabetes · Active Member

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    Hi,

    I bought a Libre Sensor from Boots yesterday (£64, and they wouldn't remove VAT).

    Applied yesterday, and got readings after 1 hour. Everything seemed fine.

    A day later, I am getting completely wild readings.

    Before breakfast, the Libre sensor is reporting 6.6.
    90 minutes after breakfast (bacon and coffee, so very little carbs), the Libre sensor is reporting 8.1 then 8.8 a few minutes later.

    My glucose blood tester is reporting 6.2 and then 6.4.

    Surely, there can't be such a large difference (2.4), so is the Freestyle Libre sensor so inaccurate that it becomes pointless, or did I just get a faulty (and expensive) one??

    Thanks,
    T
     
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  2. urbanracer

    urbanracer Type 1 · Expert
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    Remember that the Libre is 15 to 20 mins behind blood glucose measurements. (10 mins according to their literature) so if your blood glucose is moving sharply up or down (like maybe after eating) then you may see a bigger difference.

    Compare your readings when the Libre is showing a flat(ish) line.

    I have found though that my sensors have been inaccurate below 4 and above 9. They may also take 24hrs to 'settle down'. I've seen people on the forum write that they don't activate them until 24hrs after application to maximise the 'useful' time.
     
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  3. TedTomato

    TedTomato Prediabetes · Active Member

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    Thanks. I have measured over a period of an hour, and I am getting a difference of more than 2 mmol/L between the sensor and my regular blood tester.

    Given the breakfast I had (hardly no carbs) and no food for the previous 10 hours (with very little carbs for dinner), there are no reasons for glucose level to spike so much.

    I understand that it could take 24 hours for the sensor readings to stabilise, but I haven't seen such disclaimer on their website or app. If they know the readings can be quite random for the first 24 hours, then they should indicate so (and maybe not show any results)!

    Hopefully, the readings will come closer to my blood tester, else this is completely useless.
     
  4. hankjam

    hankjam Type 2 (in remission!) · Well-Known Member

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    This would be disappointing as the amount of R&D to bring this product to market would have been wasted. It has been found to be "a good thing" by a lot of forum members.
    I would give it a couple of patch cycles and see how it goes.

    £64 sounds better than I though it was, I was thinking it was around £100 at the moment. Been thinking about but don't have a smart phone, which would be an additional cost.... :(
     
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  5. urbanracer

    urbanracer Type 1 · Expert
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    The libre starter kit (£120 ish) provides everything you need to get started - you don't need a smartphone.
     
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  6. urbanracer

    urbanracer Type 1 · Expert
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    I take your point, but what happens at home is never (well probably never) going to replicate what happens in a lab.

    It's interesting that many people on Facebook post similar comments on Abbott's advertisements. I posted that the Freestyle kept telling me that I am hypoglyceamic when my blood glucose is actually +4. An anonymous response told me to get in touch with their customer relations people., I couldn't be bothered. You may get a free sensor out of it if you try though.

    If you look at the info sheet that comes with the kit, something like 12 to 15% of readings do not correspond with a reference finger prick test - I'd say that broadly reflects my experience and probably indicates why DVLA have not approved it yet.

    As for being completely useless, I'd have to disagree. The finger prick test is a snapshot in time, the Freestyle shows trending information which I find invaluable.
     
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  7. Fleegle

    Fleegle Type 2 · Well-Known Member

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    The starter pack which contains a reader and two sensors is £159 then you can get VAT off so that should be more £130 - from libre themselves, Then the sensors cost £58 then you can get the VAT off so that is about £46 a sensor which lasts 14 days.
    I budgeted £100 including VAT a month and got a little change as I often found a free postage coupon.

    You do not need a smartphone. You can access all the information on the device for realtime, trend and some summary 90 day data and I found that generally was all I needed.

    If you have a desktop or laptop PC then you can connect the device to that and download the data into its free application and run some pretty good data - lots of reports.

    If you are savvy and have nothing else to do you could download as a file - put into something like tableau and produce graphs till the cows come home. I tried this for a while before I realised that the stuff that came out the box told me more than enough.

    The device allows you to mark when you eat and can remind you to do a 1hour and 2hour post meal check. When you look ta the graph online it will mark and display the post meal high. I found this most useful as sometimes I was going higher earlier than I thought I was - so my down curve happened earlier which was really helpful when I did the ND.

    Anyway - sales pitch over. I want to add that I do not own shares or have any interest at all in abbottt :)
     
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  8. bulkbiker

    bulkbiker Type 2 · Oracle

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    There have been various other threads that recommend leaving the sensor attached for 24 hours before taking the first reading.. I have no personal experience of it but this may be another reason yours seems out.
     
  9. Fleegle

    Fleegle Type 2 · Well-Known Member

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    There should not be a 2 difference.
    I guess what you do not know is which one is most accurate. Both could be 20% out so the actual median of the two could well be in target range. But that said - I wouldn't expect it to be 2 out.

    As a worse of all options, if it is constantly 2 out - and you think your meter is pretty accurate then just self calibrate. Deduct 2 from the sensor. Not ideal but saves a wasted amount of money.
    I used the sensors for about 7 months constantly and I would calibrate myself every day a couple of times - usually when the sensor went high on the hope it was lying. Unfortunately it and my meters were all agreeing more or less.
    Or send it back to Abbott they will probably refund. Ring them - do not remove it until you have made the call.

    As for the zero carb but still a rise - that can be for many reasons including dawn phenomena though I see your tag says pre-d so I would of thought that unlikely.
     
  10. hankjam

    hankjam Type 2 (in remission!) · Well-Known Member

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    Hi @Fleegle
    A useful and informative post. Not needing a smartphone will be a blessing as my very old Samsung flip up does all I need a phone to do. :)
    I've stopped doing the lottery and started to "invest" in Premium Bonds.... some of that might go to support a Libre... though it would not cover too much of it.
    Cheers
     
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  11. TedTomato

    TedTomato Prediabetes · Active Member

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    I will have to check over the next few days, but if it's giving random figures, higher by 2.5 mmol/L than my other blood testers, then this is useless, either for spot checks or for averages.

    I have tested over the last 2 hours, and the sensor is still 2 mmol/L higher, so that's going to impact averages too if such inaccuracy is sustained for long periods.
     
  12. Fleegle

    Fleegle Type 2 · Well-Known Member

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    I found that the 24 hour thing didnt make tons of difference but in the end I thought why not and put one on 24hours before the other expired, You do not activate it so 1. you don't know if it makes any difference and 2. you don't lose any days as it lasts 14 days from activation not from application.
     
  13. TedTomato

    TedTomato Prediabetes · Active Member

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    Thanks. I will contact them tomorrow, and ask for a replacement if numbers are still out.

    It could just be a faulty sensor, and I would like to pursue the option of "constant" monitoring, as I would like to see if I have hypoglycemia during the night, or the impact of eating specific food.

    When I activated the sensor yesterday, it reported a 5.2, which was actually quite low, so I am not too keen on just deducting 2 from the results.
     
  14. TedTomato

    TedTomato Prediabetes · Active Member

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    I don't really get the point of placing it but not activating it. Surely, if it's not activated, it's in standby mode and not reading anything (otherwise, it would self activate once inserted). Therefore, what difference would that make??
     
  15. urbanracer

    urbanracer Type 1 · Expert
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    It has it's own button cell battery so it's powered up and working. It will not send data to your reader though.

    The idea is that you give it time to sort itself out on your body - whether this is effective is open to debate.
     
  16. Fleegle

    Fleegle Type 2 · Well-Known Member

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    I agree - it measures the fluid just below your skin so bleeds - or the disturbance of placing it in could cause it to fluctuate. The idea is that it settles down. like @urbanracer I have no proof whether it works or not - my own opinion is sceptical other people swear by it.
     
  17. mountaintom

    mountaintom Type 1 · Well-Known Member

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    Mine was around 2 points higher for the first ten days. Now it’s about to drop off (15hrs left) it’s been spot on. Don’t know why. I initially didn’t rate it but now that it’s about to expire I think I’m going to miss it. Ordering another 2 but will probably have to wait a month for delivery. Useful for checking lows/hypos in a hurry or if I’m outside (work outdoors).
     
  18. LooperCat

    LooperCat Type 1 · Expert

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    The reasoning is that it gives your immune system time to respond to it, and decide to ignore it.
     
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  19. Scott-C

    Scott-C Type 1 · Well-Known Member

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    Because of this:

    "....sensor insertion causes trauma to the insertion site. It can disrupt the tissue structure, provoking an inflammatory reaction that can consume glucose followed by a repair process. The interaction of the sensor with the traumatized microenvironment warrants the need for a waiting period for the sensor signal to stabilize, and that period varies depending on the sensor type"

    www.ncbi.nlm.nih.gov/pmc/articles/PMC2903977/
     
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  20. TedTomato

    TedTomato Prediabetes · Active Member

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    If the sensor insertion can consume glucose, does that mean the level measured would be lower then?

    All my readings are significantly higher than what they should be.

    Also, if the manufacturer knows that the first day or so could lead to random results, why don't they just discard the first day of results? There does not seem to be an option to discard readings/periods
     
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