My Dexcom 7 CGM and I have had nine days and nights together and we’ve parted ways. And, as if it knew I was not happy with it, it gave me one last kick in the teeth coughing up its last numbers.
I met a friend today for brunch in Manhattan. I walked from my apartment in Brooklyn over the Brooklyn bridge and then took a subway to the cute little Italian bistro where we were meeting. The walk took about 90 minutes.
After being seated and looking at the restaurant menu I took out my meter and tested. I was “80.” I took the CGM receiver out of my pocket. I was “80.” Unbelievable! This is the first time since CDE/Pump Trainer, Gary Scheiner, slapped the sensor pod on me last week in Philadelphia - and I carried it across state lines - that both showed the same number.
I know the CGM’s numbers are not expected to match up precisely with your meter numbers. I know the CGM tests interstitial fluid and not blood glucose and there’s a difference. I know there’s a lag time on the CGM of 15-20 minutes. I know you’re not supposed to make dosing decisions off the CGM. I know that meter readings vary up to 20%. I’ve also learned that means if you test on your meter and get 80 and you test immediately again, you might get 80 or you might get 68 or 92 or 104. I know all this, yet after its first week of so many misses, the CGM immediately won back my trust, and my hope, with that "80."
Two hours later after a fairly low carb lunch my friend and I were strolling around and the CGM read “180.” Hmm…I thought, well I did have a few roasted potato pieces and a half a plain cookie the waiter brought along with the bill, maybe I need another half unit, so I took it. Then my friend and I spied a new concept yogurt store where you make your own frozen yogurt and toppings so of course we had to go in and see. And we had to put that tiny paper sample cup under the raspberry and peanut butter yogurt.
Now walking back to my friend’s car I reached into my pocket to see what number was on the CGM. It said “222.” Hmmm…well I had just had what was probably a quarter cup of frozen yogurt, guess I need another 1/2 unit, which I took.
Sitting on the subway platform 15 minutes later waiting for my train home a thought came barreling through my head…hmmm…“222” … I’m hardly ever over 200. Let’s see what my meter says. My meter said, “108.” My meter also said, “What the hell are you doing dosing off your CGM!!! You know better than that!!!” Surely I do, but I had forgotten in the romantic glow of that “80” when the CGM won my heart back at lunch. I so wanted to be in love with my CGM just like the many people I’ve talked to are with theirs.
I pulled the CGM display out of my pocket and went to enter the “108” to calibrate it and it gave me an error reading. It actually said, “ERR” which is just how I felt, especially if you add a few exclamation marks, “ERR!!!.” When I got home a half hour later, I looked through the booklet and saw my sensor was done, and it had had the last laugh all the way to its untimely end.
A CGM? Not for me. Not until its accuracy is twice what it was for me. About 50% of the time it was tracking 10 - 20 points apart from my meter, the rest of the time it was anywhere from 20+ to 75 points away. It alarmed me telling me I was “53” when my meter said “85” and it fooled me into trusting it so many times.
I wanted to love you CGM, truly I did. But I’m going to wait til another generation or two comes along. Until a CGM is really ready to love me back. For now I’m sticking to finger sticks, and running for the juice!
To be honest, Alan, Dexcom does have a great reputation and may well work better than the other CGMs out there currently. And I only tested one sensor and people say some work better than others. That said, if more people have more experience with Dexcom, please chime in.
I really like the Dexcom (I am currently out of sensors and hoping I can get more). I have had some bad sensors though. Quality is better than quantity when it comes to calibration – if you calibrate too much trying to get the Dex back inline, you can actually make your readings worse. Last summer, I was starting to calibrate more and my readings kept getting worse. When I went back to 2 calibrations a day, the readings greatly improved. It is also better to only calibrate when your BS has been stable for at least 15 minutes. If you are dehydrated, that will throw readings off – with the heat we have had, that could have been part of the problem for you. I think dehydration was part of the problem that I had last summer.
Humor with a slice of real life. Funny!!!
Lois
lol.so true.
when its right its right.but when its wrong it is really really wrong.there is something major wrong with wearing something that i have to check…and recheck.sadly im coming to a few conclusions.15 min lag time does not seem like a long time
but it can be,i test a hell of a lot more now because it freaks me out. when im at 138 and it insist im at 220 i want it to accept what i tell it. after putting in a correct number from the meter and its saying “no you are at 208 now!”
a meter works for every one.a cgm does not.
when the sensor does not get right for 2 days it cause me a lot of fussing.i dont really believe that the extra 15 hrs a week worrying about what its saying is a benefit to my mental health. nor can i get behind the thought i have to keep looking at it every 20 min to see the trend arrow. i need it to work all the time every time.it has to be dependable
and nothing like this should have to have support groups to make it work right or to have 20 pages of tips and tricks…
When I first talked to my pediatric endo about getting Eric on a CGM, he asked what I hoped to get out of it. “Something that will tell me when he’s going high or low before he gets to an extreme,” was my answer. “You won’t get that,” was his reply. What I WOULD get, he told me – and experience confirmed it – was a better understanding of Eric’s trends, and something that would alert me if the trend was changing rapidly in one direction or another. Yes, the sensor is sometimes way off of the real number; yes, there are times when the sensor tells me he’s at 104 when he’s actually falling below 74. I don’t worry so much about the numbers; I look at the graph. That’s where I get most of my information and it has helped me enormously in getting and maintaining control. (Which isn’t to say that I haven’t also been foolish enough to dose off the CGM, regretting it later.)
Nicely written! I couldn’t live without mine. I’ve used Dexcom four years. I still stick my finger 10 times a day. Simply knowing if you are trending up, or trending down is a huge factor in making dosing decisions. And after time, and dozens of sensors, one knows if the unit is off or not.
I agree with Joe, now that I have it I wouldn’t want to live without it. But I have noticed that if my BS is spiking around it will become inaccurate. So in your example of frozen yogurt, that would have spiked me(unless my starting BS was 50), so once the Dexcom spiked and came back down it would probably take awhile for the Dexcom to come back in line. Once my BS leveled off for awhile, I would probably recalibrate.
I have a Medtronic, but the issues are the same. Some sensors are fantastic, and some are duds. This is a product in its infancy, and will most likely improve in the future, just like meters got better and better over the years. So you probably made the right decision, Riva.
And by the way I laughed when I saw that you wrote “intestinal fluid”. You actually meant “interstitial fluid”. You REALLY don’t want to deal with intestinal fluid, also called chyme!! 
You are absolutely right about my blunder Natalie and I forgot to correct it ;-0
Thank you for writing what I have thought and experienced so many times, Riva! I still use my Dexcom much of the time, but often question why I bother. And I, like Natalie, really enjoyed the wee slip about intestinal fluid
OK, gurls, shamed twice, I corrected it! 
It helps if you remember that the glucose level in interstitial fluid (and yeah, I got a giggle out of “intestinal” too – sorry Riva, you’ll never live that one down) ahem INTERSTITIAL fluid tends to lag behind blood glucose by rather a lot, so if your BG is going up or down quickly, it makes absolute sense that the CGM will not reflect the real status of your BG. If I take my son’s BG and it is 30 or 40 points behind or in front of the CGM, what that tells me is that the change in BG took place over a very short time – meaning, I probably didn’t bolus him soon enough before he ate, or that I gave him too much to correct a high and he came down very quickly. If it happens a lot, it cues me to upload his pump and look at his two-week or four-week trends to see if maybe there’s a pattern that could indicate a need to change his basal rate, his carb ratios, or his correction factor.
First, let me state that I know nothing about what you are talking about…but I do know meters, food, exercise and readings that don’t match. I have two regular glucometers that I use regularly. The first is wonderful, but it reads at least 20 points higher every time…my second, and the one I have had for over 6 months, reads a more accurate reading that matches what the docs office shows. So who do I believe, the doc’s meter, my second one, or the first one? Don’t know…do I take an average? Nope I go with the 6 month old one, because even in testing I get better readings. All of this is horribly frustrating for those of us who have to rely on instruments to tell us how we are doing…frustrating, and possibly dangerous. I feel you pain, and hope that you have found a method to keep yourself safe and stress free. Why oh, why can’t meter makers of any kind find one that works 99% of the time accurately.