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Spot Off.

Party time, in a decidely un-party time sort of way.BEEEEEEP!  BEEEEEP!  wails the Dexcom.

Birdy, who is coloring at the kitchen table, yells back, “BEEEEEP! BEEEEEEP!  Mawm, your Dexcom is making the beep sound again,” and she absently points her red crayon towards the bottle of glucose tabs on the table nearby.

For the most part, I can rely on the Dexcom to be accurate when it’s throwing out results to me.  Low alarms are ones that I take very seriously, as well as the double-down arrow alarms, because they need immediate action.  My blood sugars tumble fast once they’re under 70 mg/dL, so when the CGM hollers to warn me of an “UNDER 65 mg/dL,” I can pretty much guarantee that the “LOW” alarm is the next one on tap.  High alarms are also taken seriously, but not with the same immediacy.  I will finish driving somewhere before correcting the high, whereas a low makes me pull the car over and treat.

Point is, I trust the CGM.  A lot.  More than the FDA and the owner’s manual says I should (no, I don’t always test to confirm a low because I’d rather take the chance of the CGM being slightly off than take the chance of face-planting in the backyard).  While the data was overwhelming at first, I’ve come to rely on it, and it helps shape my diabetes decisions throughout the day.  My health is – dare I say? – better as a result of wearing a second, sometimes clunky-ass device.

But when it’s wrong?   I’m tweaked out and frustrated, spoiled by the accuracy and precision I’ve come to expect from the sensor.

Yesterday morning was Dexcom Replacement Morning (i.e. the installation of a new sensor, peeling off the week-old Toughpad/transmitter combination that looks and feels as if I’m removing a 90 yr old skin graft after so many days stuck to my thigh), so I knew that the receiver data might be a little off for a few hours (seems to be standard for me).  However, by the time I went to the gym that night, I’d been wearing the sensor for at least seven hours, and had calibrated it three times.  My meter said 217 mg/dL before walking into the gym, and the Dexcom confirmed the same range, in an ish-y sort of way, with a 250 mg/dL.

Since my blood sugar was high and I was feeling sluggish, I opted for the stationary bike instead of a treadmill run, and after the first 3 minutes, I noticed that the Dexcom was trending down.  But not crazy-down.  More like comfortable, exercise-expected down, with a 190 mg/dL and a southeast-facing arrow.

About fifteen minutes later, I noticed that I was sweating a lot.  More than usual.  And it wasn’t “workout sweat,” which seems to come in at a steady pace.  This sweat felt pulsing, like it was a flash flood of panic, and within a few minutes, my forehead was slick and even my elbows were damp.  The Dexcom said I was 200-and-something with double-down arrows, but my body was sending me an entirely different message.  Which is why I wasn’t surprised to see a 70 mg/dL on my meter.

Lips numb and counting out five cherry glucose tabs from the jar (putting them all in my mouth at once while I was counting, and then realizing I should probably eat them one at a time), the low wasn’t quick to give in to the sugar onslaught, giving me plenty of time to question my trust of the CGM.  I don’t want to consider the Dex “only as good as it’s last result,” but missing a low by almost 150 points has shaken my confidence in this particular sensor’s accuracy.

My Dexcom is like the little girl with the curl on her forehead:  When she was good, she was very good, but when she was bad, she was horrid.  Thankfully, I get more good than horrid, but it will take me a few days to regain trust.  In the meantime, I’m leaving a trail of extra test strips in my wake.

16 Comments Post a comment
  1. ish-y!


    i don’t want this to be true. when our dex is off, i’ve always been able to attribute it to the settling-in phase.

    05/22/13; 11:59 am
  2. Dan #

    Hi Kerri,
    After changing to a new sensor unit, how many blood glucose value do you load into your dexcom receiver? One choice is to take the opportunity to load a batch of actual blood glucose readings across the period of the first day. Meaning one for the first four hours. Now, my suggestion regarding the use of Dexcom Studio. Contained within the program is a report entitled, “Hourly Stats”. The thin blue lines present the range of values from the sensor verses your actual blood glucose values. And, give some consideration to loading data into the Events section on the receiver. Activities which have the potential to result in rapid changes in our blood glucose levels would be the ones to add. Meaning, post the start of your exercise and meals. These periods could result in quick movement of blood glucose levels and the time required to balance the glucose levels between the blood stream and the body fluids which is where the sensor is positioned. Hope this helps and as always have a great day.
    PS Am looking forward to hearing about your review on the Studio software.

    05/22/13; 1:08 pm
  3. Sally Poutiatine #

    It both cracks me up and confounds me when my T1 daughter stuffs 4-5 glucose tablets into her mouth… I’m pretty sure 5 is her maximum capacity. Nom nom…

    05/22/13; 1:59 pm
  4. I rely on my CGM more than I should, too. (In fact, this morning I was driving in my car, CGM showed a steady 100-105 range, but felt a bit “off” and discovered a not-so-startling 68 mg/dl. I took care of it on the spot). I’ll caveat this by admitting I use the archaic great-grandfather of Dexcom G4 (aka Medtronic) which isn’t quite as accurate.

    Nonetheless, I believe treating to a CGM is generally not a big deal, provided you have a trend. Highs and lows shouldn’t come as a surprise, even though “how high” or “how low” may vary (in fairness, you DO have two down-arrows in that picture).

    05/22/13; 2:29 pm
  5. Hi Kerri 🙂

    I’m also using a Dexcom G4 and experiencing some “off” values the first day wearing my sensor. However, I don’t mind these off values as long as they’re not too off as you experienced when working out.. The most frightening ting aout the Dexcom is the two falling arrows. I’ve actually become really scared of them, and my potential lack of ability to treat the coming low quick enough. It’s become an awful anxiety ruining the overall benefit of having the Dexcom at all.. It’s like you say, when it’s good it’s really good and the opposite. I often call it my best friend or my worst enemy. Anyway, do you have (or anyone else) any advice for me how I can get rid of this anxiety for the vibration and beeeeping of the falling arrows? I don’t get afraid when I’m low, I can handle that, but I’m afraid of not having control, I guess..

    Best wishes <3

    05/22/13; 3:26 pm
  6. Ellen #

    If you are hearing BEEEEEEEEP BEEEEEEEEEEP you are high. It is BEEP BEEP BEEP when you are low!

    On a serious note it frustrates me to no end when I am 100+ points off between Dexy and my meter. Dexy pretty consistently thinks that I hit 75 or so at 5am. When I test I am at 126ish. I hate that this thing wakes me up all the time- but I hate that this disease could keep me from waking up at all.

    05/22/13; 3:43 pm
    • LOL!! You’re right. It’s BEEP BEEP BEEP all the way for the lows. Birdy knows the difference. Clearly, I’m spaceshot. 😉

      05/22/13; 4:21 pm
  7. Kelli #

    Kerri, you rock. I love that someone else admits to having a 217. We’re diabetics, not robot versions of pancreases (although sometimes it seems that way). You just made me feel a heck of a lot better about my 220 today!! Thanks for the post 😉

    05/22/13; 4:00 pm
  8. Here’s a picture of MY girl with a curl in the middle of her forehead!

    I never did learn to trust my CGM during pregnancy- it was off by 100 points a lot. I test drove the new Dextrom with similar misreadings.

    Glad you are OK, Kerri! Those lows really shake you up.

    05/22/13; 4:39 pm
  9. Would you recommend a CGM to someone who is trying to get pregnant? I’ve only had my pump since February, and passed up the CGM because originally I was told that the sensors would cost me $600 every 90 days.Now because of billing issues with Medtronic I’ve been talking to the regional manager of Medtronic and he is telling me that they will be much less. I’m kind of considering a CGM but when I read reviews on them and blogs like yours that they give so many errors I wonder if it would really be worth it.

    05/22/13; 5:41 pm
  10. Dan #

    Hi Kerri,
    There is another factor which can impact the readings from our Dexcom G4 Pt.
    The product Tylenol can really mess up readings. Or, to be more direct is any medication which contains Acetaminophen. There are other medications which contain acetaminophen. The term the pharmacy uses for this conditional medical impact is referred to as a Contraindication. Hopefully your pharmacy has been notified of this fact. As always have a great day.

    05/22/13; 9:10 pm
    • Yes, I’m very aware of the Tylenol conundrum. Wasn’t a factor this round, though. 🙂

      05/22/13; 9:35 pm
  11. V #

    I always wait a good 30 hours to rely on it. Before that, it can be right but to my opinion, it still doesn’t respond fast enough to big variation.

    05/22/13; 9:24 pm
  12. Karen #

    My daughter and I say that the Dexcom is slow to catch up and this, of course, is especially true during a rapid rise or drop in blood glucose. SO…like at the mall the other day (I should KNOW by now to do a temp basal while shopping!) she was finding a spot to sit on the floor maybe just 2 minutes after saying, “Hmm, I don’t feel good” and Dexcom said 94. Then the very next reading it alarmed at 66. Really? nearly 30pt drop in 5 minutes? Weird. But still is better to have IMO…sometimes she doesn’t feel the lows that quickly and can be in the 40s before she does. For the times that it is “Spot Off” I think there are probably 20 times more that are “Spot On”.

    05/23/13; 10:58 pm

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