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FreeStyle Libre: why does it last 14 days?

Discussion in 'Ask A Question' started by Catarina Gomes, Oct 19, 2018.

  1. Catarina Gomes

    Catarina Gomes Type 1 · Member

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    Hey everyone,
    I am making a report for a biology course on artificial pancreas and as a part of it, I need to know why does FreeStyle Libre lasts 14 days and no longer than that. Is it a tissue response? Do you have articles or sources of where to find this information? I was unsuccessful to find this.
    Thank you.
     
  2. Squire Fulwood

    Squire Fulwood Type 2 · Expert

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    I don't know the answer to your question but I know that in the USA they only last 10 days. I find that a far more interesting question. Obviously the manufacturer can choose how long they last within reason but I don't know what would happen if they chose to make them last longer.
     
    • Informative Informative x 1
    #2 Squire Fulwood, Oct 19, 2018 at 4:11 PM
    Last edited: Oct 19, 2018
  3. xfieldok

    xfieldok Type 2 · Well-Known Member

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    Ask the manufacturer.
     
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  4. becca59

    becca59 Type 1 · Well-Known Member

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    Ha ha! My guess would be to make enough money, 14 days is the optimal. Cynical!!! And £90 a month poorer. Just to ensure I’m as fit as can be and as productive in society as I can be.
     
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  5. Deleted Account

    Deleted Account · Guest

    I don't know but suspect it is a combination of commercial, medical and regulatory reasons.
    If the sensor lasts too long, we will not buy any more. Maybe they could make them last longer but the cost of doing so may be difficult to recoup.
    I have found the accuracy and reliability seem to start to drift towards the end of the two weeks. I think this is due to small movements of the sensor.
    Different countries have different regulations for all sorts of things and I would not be surprised if this is the reason they last less time in the US.*

    As a component of an artificial pancreas, other CGM may be more appropriate as some of these last longer than 14 days (but cost more). For example, the Eversense lasts months.

    *The Epi Pen shortage is due to regulations changing in the US. These should not affect other markets where the regulations have not changed but as they are manufactured in the US, the manufacturers have to change their process.
     
  6. Gaz-M

    Gaz-M Type 1 · Well-Known Member

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    I can get an extra few hours ( around 7 ) with the Miao Miao
     
  7. Scott-C

    Scott-C Type 1 · Well-Known Member

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    It's programmed to cut out after 14 days and that will be partly a business decision, but another reason is that the sensor filament has an enzyme called glucose oxidase on it which oxidizes passing glucose, breaking it down into other chemicals, the breakdown gives off electrons which are measured as an electronic current which is then turned into a reading: more glucose, more electrons, more current, higher reading.

    Over time the glucose oxidase wears out and the sensor will start to fail. We know that Dexcom users can get much more out of a sensor than the official 7 days, sometimes 2, 3, even 4 times as much and they then notice the readings start to get noticeably more erratic and noisy.

    Part of that will be the glucose oxidase wearing out and also "biofouling" - the filament basically gets clagged up with biological detritus so the glucose can't actually get to the filament to he measured.

    No one has yet been able to hack libre to get more time out of it (xDrip+ will get an extra 12 hours but that's as far as it goes).

    Based on what we've seen with the dexcom hacks, it's pretty clear that a libre sensor could run for longer if someone found a way, but Abbot has likely done some number juggling and decided, not least to get approval, 14 days is a safe bet to (a) keep profit levels up and (b) stop it before the oxidase wearing out and the biofouling starts giving sketchy numbers.

    It's 14 days here but in America it is (or was, not sure if it's changed now) 10 days - they wanted FDA approval for bolusing from it so they had to cut it to 10 days. I expect that was because the FDA was saying after 10 days, it gets shakier.
     
    • Informative Informative x 3
    #7 Scott-C, Oct 19, 2018 at 7:09 PM
    Last edited: Oct 19, 2018
  8. Scott-C

    Scott-C Type 1 · Well-Known Member

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    There's a lengthy paper, "A Tale of Two Compartments", at the link below which discusses a lot of the reasons why sensors have to be time limited. It gives a good overview of the challenges involved - at the end of the day, a sensor is a foreign object which isn't meant to be there, so the body tries to reject it.

    It was written back in 2009, and the technology has moved on massively since then but the main points still hold true.

    https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2903977/
     
    • Informative Informative x 1
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