T1 Weirditude, CGM edition

Got my 1st Dexcom back in April, so I’m still sort of a newbie. Mostly it’s been tracking pretty close to fingerstick results. This morning though… not so much. Only the weird thing is that the CGM result makes a LOT more sense than the fingerstick one does.

So, I ride my bike to work. Biggest problem is managing the lows for this so I don’t arrive at work with a hypo to deal with. I actually run “Share” to my iPhone while riding. I have an iPhone holder on my handlebars and I can watch what my bg is doing in realtime–handy! So my BG (fingerstick) at departure time is 118. I can easily drop 30 pts from the ride, so just to be safe I started a temp basal to stop delivery for 30 minutes. By the time I got to work the CGM is showing 80, just about what I expect on previous experience, not bad, definitely feeling “low” but I know there’ll be a bounce-back and I’ll probably be in the 100 neighborhood soon enough. Get to my desk and do another fingerstick for the sanity-check… 144! Wha? Try again, just in case… 148.

Nothing out of the routine this a.m. food-wise, and if you’d asked me to guess my level without looking, 80u is about what I’d have said based on experience but also on sensation. I mean, I have to go with the glucometer, but I’m really surprised not just at how big the discrepancy is–the largest I’ve seen so far–but the odd thing is that it seems like the CGM has it right this time.

This has been another episode of “No Matter How Experienced You Are and How Much Sophisticated Gear You Have, T1 Is Always Weirder Than You Thought”


Did you wash your hands & use a different hand/finger for follow-up test? (I am required by my OCD to ask this :anguished: :triangular_ruler: )

I look forward to the next episode where hopefully we learn what happened next. :confused: :cat:

Well, the fingersticks have it. Checking again before heading out to lunch and it’s 138. My guess fwiw is that the CGM-lag and the Dexcom’s tendency to exaggerate lows may account for part of the discrepancy anyway. I was trending low when I left, which is why I programmed the temp, but maybe the temp wasn’t necessary and so BG was going up during the ride (though that’s not what it USUALLY does even with a temp) and CGM was slow to pick up on it…? Sometimes this stuff is like figuring out Nostradamus’s predictions: they none of em’ make any sense until AFTER the event (and not even then really). If I’d known where I was going to end up I would not have set the temp basal–apparently I would have been fine without it.

But how do you know??? All my data and recent experience indicated I should do what I did. It’s not that I ended up in such a terrible spot, of course but still. Sometimes I just want to yell “THIS IS TOO COMPLICATED!” Having an in-range reading is normally a good thing, but having it at the beginning of my rides is actually a problem, because even if I set a temp basal to zero for the duration of the ride, my BG is going to be in the red by the time I get to the end. I really hate having to eat a bunch of dextrose tabs before going for my bike rides–seems rather self-defeating–but ensuring that my BG is just arriving around 120-30 at the time I’m planning to go is very hit-or-miss.

when in doubt with fingersticks, either do another test (if you think the reading is falsely high, wash hands and retest), or use another meter if it seems way, way off of what you expect. One thing I must say about the Contour Next, for all of it’s faults (and there are many), accuracy and repeatability, are the best of any of the meters I’ve used since the mid 1990’s and that’s a lot. To think I relied on the falsly high readings of my many Compact Plus meters is scary. When I’d get up near 200 in the past, those meters skewed all of the readings higher than the actual bg. No wonder I used to get hypo when correcting using those meters. So now I exclusively use the crappy, but accurate (IMO) Next. It better follows the readings from the Enlites, than any other meter I’ve tried.

Good advice of course. I have a spare meter at work but it’s currently out of strips so I just tested twice with my regular one. Which IS a Counter Next, coincidentally, and I’ve been pretty happy with it. Came with my Medtronic pump, but I’ve still been using it after switching (temporarily, it turns out) to a Snap. Of course it complains about failing to contact its paired Minimed, but soon enough they will be reunited, alas.

You can turn off the “feature” to automatically attempt to forward the results to the paired Medtronic pump in the settings of the Contour Next.

I have actually done that because I like being able to pick when the meter is going to throw the BG result in the general direction of my pump. My current Contour Next BG meter settings are:
    Settings > Pump Settings > Send Options > Ask Me
The other two possibilities are Always (the default?) and Never.

Turns out I am pretty much a “middle of the road” kind of guy in apparently just about everything. :blush:

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I feel ya! Circadian rythms??

I went on a ride two weeks ago that ran a perfect (and unheard of) flat line around 80mg/dl. I ended the 0% TBR about 30 minutes before the end of the ride, ate a meal and watched my BG climb to a new flat line around 180mg/dl. Bolusing would seem to have an effect as I would see the CGM or meter drop to 170mg/dl (all with the sideways CGM arrow). I finally changed out the not quite 2-day old infusion set, performed a correction bolus and … VOILA!

Thanks man, there are settings–who knew? As my wife says, she a senior LINUX/UNIX sysadmin, MA in EE, and general smart person: “RTFM.” But I’m a guy, what can I say, and as we all know the official Guy Motto is “Never ask for directions!”

I changed infusion sites last night, so that can always be a possible source of weirditude. Should be a good one though. I’m trying using my lower back, which has been untouched since I switched from MDI two years ago and it was always a good spot for injections. But in the words of the immortal Fats Waller, “One never knows, do one?”

I actually can’t remember how the heck I stumbled across that. Perhaps I was reading something online?

Though sometimes, if no one is watching, I actually will read bits & pieces of the manual — probably to enjoy the feeling of wickedness it gives me because I know I am really not supposed to do that! :smirk:

My multivaried and dubious past includes a stint as a tech writer for a biotech instruments firm. The main thing I learned there was that the primary purpose of the operator’s manual was to force engineers to decide things. I got a publication date, I gotta write something down, so what’s it gonna be guys? Instructing people on how to operate the dingus was merely a side-effect.

Well let’s just see how the homeward commute went then, hm? Running pretty high all afternoon (163 @ 3:45) so we’ll just leave the pump on, not that long a ride, should be ok. Bit of a rush, didn’t set up my app to watch the Dexcom, but ok, only a 25 minute ride, what could possibly go wrong? M’kay, it buzzed an “80” alert in my pocket about halfway home. But then it’s always overreacting right? I’m betting on Mr Contour–this ride doesn’t normally knock things down that much. Mr CGM more or less agrees, reading “72” when I get in the house, not unusual after a long ride, maybe not so usual for this one, but not totally off the wall either. Anyway Mr Contour Next will surely correct Mr Dexcom for his hysterical behavior with a good solid 100 or so, if this a.m. is any guide. Hm… GULP. Mr Contour Next thinks Mr Dexcom is being some kind of low-BG pacifist, weighing in with a bright orange “60.” Re-checking after 5 minutes: “56.” Mr Dexcom now agrees, so that’s something: “55” with a down-arrow. Guess I better do something about that. Guess that temp basal that was a wrong idea this a.m. would have been a much better idea this afternoon. Not sure why exactly…

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If I had a nickel for every time that thought has crossed my mind … :smiley:

BTW, we are just past the full moon and there is a strong gravitational effect on the delivery of insulin under these conditions!

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Far be it from me to discount the influence of astrology over all aspects of existence–well, that and ancient aliens obviously–but I think I’m coming around to the opinion that @YogaO was right with that circadian rhythms thing. Not sure it make sense of the CGM-glucometer discrepancy in the morning, but it definitely figures into the question of whether or how much to set a temp basal, a.m. vs p.m. I’ve always had a pretty big struggle with “dawn phenomenon” and from what i’ve read recently it actually lasts later into the morning than I’d always assumed. So that’s probably still exerting enough upward pressure in the morning that the temp isn’t really necessary, whereas in the afternoon clearly it is. Though that drop during yesterday’s p.m. ride was bigger than I’ve seen even on longer rides in the evening. So there are still enough ~unexplained phenomena~ here to support both Ancient Alien and Astrological intervention I think. So that’s good news anyway. Bigfoot may figure in too, somehow. Certainly can’t disprove it, and we know from the History Channel, what you can’t disprove must be true!

@DrBB - I’m just sayin’ … gravity, the spinning of wheels with all that metal, plus I’ll bet you traveled along a path that was magnetically aligned with the North Pole (at some point) … (damn, my tongue is stuck in my cheek today!)

(less cheeky here) plus, the reduction in stress from leaving work (as opposed to the addition of stress going to work) … the joy of riding …

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All of the above plus ley lines–you need ley lines to make all that other stuff work.

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There is that, but then I think it is also complicated by aspects of what is sometimes called superstitious learning. My feeling is that it is often very hard to pull out the actually meaningful part of the pattern from the deluge of daily details which often seem just as pertinent to us.

Did you ever call Dexcom and ask “What’s up with this?” I am so used to tweaking my Enlite that I’m not sure where to go with Dexcom. I usually try to just never ask because of the potential of the question to unintentionally fall into the Mac versus PC rabbit hole.

Thanks John–or may I call you Irrational? Obviously you’re not though. I totally agree regarding separating noise from signal in this stuff. The plural of “anecdote” not being “data,” I’m trying the empirical approach. I stepped the basal down only a bit this a.m. and the fingerstick result was 123, comfortably far from having to attend my first meeting in the midst of a hypo. The Dexcom was still way under with a 90, though the discrepancy is narrower. Not sure what to make of that since it seems to be unique to this time of day. Mostly it tracks within 10-15 points, and is frequently spot-on, so yeah, a call to Dexcom might shed some light. Just going to gather a few more data points to see if there’s a consistent pattern there or just the planetary influences. Of course “consistency” is always a relative term with this disease, but you have to go with something.

I totally agree with shunning Mac-v-PC and Dexcom/Enlite squabbles. There are already enough religious wars in the world.

I’m not aware of Dexcom/Enlite squabbles. What have I missed? You’ll never hear me claim Enlite is better. I got it because it works with my pump. Sometimes it’s great and other times it’s absolute crap. Perhaps there are some here that are snooty about their choice?? Is that why you alluded to squabbles?

Maybe not as such. Kind of a general impression from various places, not necessarily here. I was surprised to read in some thread recently that this was once a pretty Enlite-only forum and Dexcom posts tended to lie forlorn and abandoned. That’s certainly not the case now. I first heard of it here.