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cgm delay question plus calibration

Discussion in 'Ask A Question' started by EllieM, Jul 11, 2020.

  1. EllieM

    EllieM Type 1 · Well-Known Member

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    OK, I have something that I've been wondering about since acquiring a dexcom G6.

    I know that some people loop (@LooperCat ?) but how does that work with the typical delay between interstitial and blood glucose levels?

    I'm currently basal/bolus (lantus/humalog). Insulin resistant (thanks T2 dad) but T1 (thanks T1 mum) :), so am on a fairly low carb diet, probably about 80g a day.

    Since getting my dexcom I've found myself doing lots of tiny bolus adjustments, but I'm really noticing the lag (there's nothing like the G6 complaining that I'm heading under 3 when I've already taken a glucotab and my glucometer says I'm 3.6). Similarly, I find it easy to bolus too much when it tells me I'm going high and actually I've just caught the peak of my rise.

    Do loopers just go very low carb so they never stray anywhere near those highs and lows and the delay doesn't matter because the curve is flat?

    Secondly, and maybe I should start a new thread for this, what do people do about calibration? So far I've found the dexcom pretty accurate, mostly not more than 10% out compared to my caresens dual (if you allow for a ten minute delay) though I'd say it under reads. Having said that, I've never been that fond of the caresens accuracy (it definitely over reads compared to the meter I used to have and love and the only reason I use it is that it is what is available on prescription in NZ and I'd have to order strips from overseas if I wanted a more accurate meter). So I don't think it's necessarily more accurate than the G6.

    Finally (maybe I should have started 3 threads?) do people always check with a glucometer before correcting lows or highs? I could easily for highs, but don't like to wait around for lows. However, I got caught horribly the other day when the dexcom said I was going low 30 minutes after injecting my lantus and I assumed that my lantus had decided to act in one rush (happened once a month ago and I had to eat 60g of glucotabs in terror while my blood sugar plummeted). I pre-emptively ate 30g of glucose. When I discovered that the vertical arrow was a fluke and my blood sugar headed for the stratosphere I had to inject 10 units of humalog to compensate. My glucometer was way more informative than the dexcom at this point and I would never had had that issue if I'd stopped to check with it before panicking.

    OK, wall of text over, thanks for any advice. And I do love my dexcom, just trying to make the best use of it.
     
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  2. Jaylee

    Jaylee Type 1 · Moderator
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    Hi @EllieM ,

    I use an MM2 Libre & XDrip. Calibration wise I look at the meter test number & count back 3 or 4 dots on my graph.. Each dot reprisents 5 minutes linear time? I only tend to check & calibrate when relatively flat. Using only my meter when low? Which seems to suggest I'm rising quicker than my set up? Gee I hope I explained that right.. Meter's have reportedly an upto 20 minute lag which is why folk can panic treating a hypo thinking nothing is happening, only to find later they over treated.?
    Though even on a steep rare curve up if i apply the same principle, it ain't far out from the meter within 0.4mmol.
    I check calibration at least once a day if I'm just rolling steady according to my graph..

    I hope this sort of helps. I suppose we all have our own "rituals."

    Edited to add; I use Lantus/novorapid.
     
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    #2 Jaylee, Jul 11, 2020 at 1:34 AM
    Last edited: Jul 11, 2020
  3. EllieM

    EllieM Type 1 · Well-Known Member

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    Thanks for your reply, it's very helpful, but either I've misunderstood or you've misworded your reply. Given that the sensor lags twenty minutes, shouldn't you be setting an alarm and checking the libre result 20 minutes after your meter reading???
     
  4. Jaylee

    Jaylee Type 1 · Moderator
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    Oooh, forgot to tag in @Juicyj , from memory, she uses a Dexy?
    We had a meet up long before lockdown with @MeiChanski . Whose patch may have been the same (I hope she OK?)
    The CGM setups weren't like mine.. There was a bit of graph flashing on devises.
    I'm pretty observant, but still don't like to stare to much..
     
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  5. Jaylee

    Jaylee Type 1 · Moderator
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    With the best intention,
    I may have Been no help at all here (headbutting 3am?) However I see consistent a slower lag than the meter with a my CGM set up coming up from a low, compared to a meter (the meter can still lag by as much as 15/20 minutes. ) than sloping down?
    I'm resonalbly receptive to Novorapid, compared to the reports of some.
     
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  6. Cobia

    Cobia LADA · Well-Known Member

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    HI EllieM i hope i can explain how a loop works ok....

    As you know there is a delay between intestinal and finger pick supposed to be aroung 10-15 min.
    Your dexcom gets a reading every 5 min with a loop setup right it calulates how much insulin is required to get to your target glucose... ideally its looking forward say 5 hours being the life of the insulin....
    In a nut shell its how all of them work. The diy loop so far works on basle only.

    On the carbs some days im VLC others 180 grams or so.
    I look at the time in range to see how im doing.

    From what ive seen with Androidaps it reduces a lot of guesswork and its working way past i could on MDI.

    All i know is for me it works good.
     
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  7. LooperCat

    LooperCat Type 1 · Expert

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    Morning! Tbh my levels don’t change fast enough for the lag to be an issue. I only have such small amounts of either carbs or insulin in my body that I just get drifts up or down, rather than hard troughs and spikes.
     
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  8. EllieM

    EllieM Type 1 · Well-Known Member

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    Thanks, not sure that would work for me, unless I went keto, which I'm not quite prepared to do yet.
     
  9. UK T1

    UK T1 Type 1 · Well-Known Member

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    Hi, I'm sorry I can't help with most of your questions, but I use the Libre and although I'm very pleased with its accuracy, I always check with a finger prick before big corrections. I'm fairly sensitive to insulin so a half unit or unit if I see I'm def running high a while later still, and know I've maybe guessed the carbs, is about all I'd do without a finger prick test to be certain. I do also get quite good hypo and hyper symptoms to go by luckily so that helps!
     
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