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Dr. Bill's Commentaries

My CGM after 10 days of experience   (October 2, 2010)

I am now using a continuous glucose monitoring (CGM) device as well as an insulin pump. Between these two devices and my Blackberry, I'm now an official gadget freak (I suspect my wife will say that I've been a gadget freak for a very long time). I've run out of pockets to put these 3 gadgets into, and am doubling up, frequently jamming the CGM into the same pocket as the pump (Personally, I don't like belt holsters for my gadgets, but that's another story).

I wrote a few weeks back about my plan to get a CGM device; I've now had the DexCom Seven Plus for about 10 days, and I wanted to give you a few first impressions.

First, although one of the selling points of CGM is that you'll get lots of glucose readings, and will have to do less fingersticks (a minimum of two per day are needed to calibrate my CGM device), I find that I'm doing more BG readings than usual, to cross-check the CGM's assessment of my glucose level against my meter's reading. As you may be aware, the CGM glucose value lags behind the blood glucose value by about 5-8 minutes, so expecting a perfect match is unreasonable. But I've found that sometimes one is higher than the other, or vice-versa, and sometimes the two readings are spot-on. It's been puzzling to me, but I'm beginning to notice some patterns: for example, if it's before lunch or dinner, frequently the CGM reads higher than the meter. I'll be watching to see if other patterns can be deciphered, but obviously, I'll be doing lots of meter-readings to confirm the CGM-readings.

Second, I've learned that my values after meals, a timeframe that I didn't test when only using a meter, frequently are higher than I had expected. It's resulted in me changing my behavior about how (and when) to give the mealtime insulin bolus: I had previously routinely given the whole bolus after the meal (when I knew how much carb had been consumed), but now I'm giving a premeal dose that's a considerable percentage of whatever I anticipate the total dose requirement will probably be, and a second intra-meal dose, and a finally, a wrapup dose when finished eating. Lots of doses, but with a pump, it's a snap to do (admittedly, it would be a bear to do with a pen or insuln syringe!). I'm already finding that this prevents some of the postprandial high values, and again, I'll be playing with this concept for quite a while...

Third, the ability to push one button on the CGM receiver and see your "current" glucose level (remember, it's lagging a bit over 5 minutes behind the blood glucose level), can be very reassuring. I can now see when my glucose level is climbing, declining, or level, and very important, when it's rapidly declining. Sure, I'll double-check the values by getting a meter BG reading, but if the CGM shows a rapid decline, it's time to react rather than risk crashing in the near future.

Next: the software is very nice, although not perfect. It's easy to use, and most of the displays are helpful. But most of the displays are about CGM values: displays that correlate CGM with other stuff (BG levels or insulin doses or other events) are minimal, and minimally helpful.

Finally, there are lots of alarms built in, most of which are optional. I can set a high level (or not bother), a low level (or not bother), a rate of change alarm, and a proximity alarm (which goes off if the receiver has been out of range of the sensor/transmitter combination for 20+ minutes).

Is there room for improvement of the device? Of course. First of all, make it cheaper. I think that it will remain a luxury device as long as the prices remain as high as they are. It's well over a thousand dollars to start, and the replacement sensors aren't exactly cheap: over $538 for 4 at one major vendor's website (that's about a month's supply if you use one per week - many people report using them successfully for over a week, and at that price it's easy to see why!). Insurance does cover much of the cost for me, but without insurance, I doubt if too many people would be interested.

I wish the proximity alarm could be set to trigger after a period of time less than 20 minutes. The device gets a glucose reading every 5 minutes, and I'd like to know if I missed two readings rather than four. The main reason the proximity alarm has gone off is at night, as I place the receiver on the bedstand, which sometimes is outside the range that the transmitter/receiver are able to talk to each other, depending on how my body is positioned while I am sleeping.

Also, I wish entering events such as insulin doses were easier (I gave up after entering the data twice, as it doesn't display on the receiver, only on the software, and even there it doesn't do anything worthwhile in my opinion). I wish it were possible to read glucose values that the CGM had generated a while ago (only the current glucose value is displayed). And when entering meter BG readings, I wish I could enter values that I did earlier: there's no ability to enter a BG except with the device's current time. (Interestingly, I can enter insulin or other events and adjust the time backwards rather than being forced to enter them against the current time.)

My overall impression is very favorable. The CGM device has already become a part of my diabetes experience, and I am a happy gadget freak.

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Dr. Bill Quick began writing at HealthCentral's diabetes website in November, 2006. These essays are reproduced at D-is-for-Diabetes with the permission of HealthCentral.

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