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Psst… CGM. We need a break.

June 1, 2009

My CGM and I are not on speaking terms right now.  I have been wearing a Minimed CGM for nearly 5 months and I have referred to it as a Love/Hate relationship.  I love that my overnight levels have been MUCH better and I love that I can glance at my pump a million times a day to see what my BG level is…. or isn’t which brings me to the hate part.  I hate how unreliable it is and how inaccurate it is.  I also hate changing the site and having another thing stuck to my body 24/7.

Yesterday I put in a new sensor and calibrated.  Tested at 185.  I was doing some work outside and was trending low.  I came in to eat lunch and soon after my CGM says I am under 40.  No, I’m friggin not.  I tested at 132.  Next comes the always enjoyable CAL ERROR.  I re-tested, entered 132 again which led to another CAL ERROR and then a SENSOR FAILURE.  Awesome.

It’s not me.  It’s you.

We are on a break.

we were on a break

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3 Comments leave one →
  1. June 1, 2009 12:46 pm

    Gary,
    I can understand your frustration with CGM. I’m between sensors right now. I tend to use one for about a week, then take a couple of days before I put another one in.
    But I think some of the issues you, and many others, have are due to having your expectations set too high by the CGM vendors.
    Here are the things they should explain better when they sell these things:
    + It is never going to tell you where your blood sugar is. That doesn’t mean it’s useless. Your A1C isn’t useless, but it won’t tell you what your blood sugar is right now. You should see the CGM as something similar.
    + It tries to figure out what the sugar level in your interstitial fluids is. (I’ll call it IF for short.)
    + It does what it does based on electrical conductivity, which is influenced by a lot of other stuff besides sugar, so they ask you to try to calibrate.
    However, unless your blood sugar level and IF sugar levels are almost the same, there is no way that calibration can work. It’s like trying to determine the temperature outside with a thermometer in your house while the furnace is going full blast.

    In one of your posts, you said:

    > 8:00 AM BG: 147 (meter), 138 (CGM)

    > Transition 1 – 9:53 AM BG: 264 (BG), 182 (CGM) Oh, great the CGM is not keeping up.

    In less than two hours, (Probably one hour, because you ate at 9.) your blood sugar went up 117 points. There’s no way the IF sugar was going to rise that quickly. Your CGM was functioning exactly as it is supposed to, and probably as well as it possibly could. It was keeping up. It was telling you the sugar level in your IF, not your blood sugar.

    > Transition 2 – 10:36 AM BG: 409!!!!!! (meter), 186 (CGM). CGM? Dude. Wake up.

    Now you were eating carbs, which drives the blood sugar up. It would elevate the sugar in the IF also, but not as rapidly.
    However, you were also taking insulin. This will lower your blood sugar and your IF sugar, but it affects the IF sugar more rapidly, because the insulin causes sugar to be taken up from the IF.
    So your CGM was right. It was doing the best it could. Your expectations from it were wrong.

    You can probably look at what happened in this blog post today and see how it might be explained.
    This technology is just not what we all wish it was. And the makers aren’t very eager to make this clear to users.

    • June 1, 2009 1:02 pm

      Thanks for the comment Jerry. Very insightful. I (sort of) understand how the CGM works, but very much appreciate your explanation. My frustration yesterday really came from the fact that it died. It didn’t allow me to restart/recalibrate/anything. It just gave up. THAT is very frustrating. I don’t like wasting those sensors. ;-)

      • June 1, 2009 3:00 pm

        if my sensor dies early (before the promised amount of time), I call and ask them to send me a replacement. If they are billing it as a 7-day sensor and plan to change $$, they should back it up. And so far, they have. I believe sometimes you get sensors that work better for whatever reason.

        It is still really frustrating, though, when it doesn’t work as well as you are used to.

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