About a month ago, I started wearing a Continuous Glucose Monitor (CGM), an ingenious device that constantly displays your current blood glucose levels, updated every 5 minutes round the clock wirelessly from a subcutaneous sensor. This is a fairly new technology but one that I’m convinced – in one form or another – will be standard management practice in the near future. 
 
As with every new technology, I expect there will be rapid improvements down the road. For that reason there are significant pros and cons at this point.  Here’s my personal take on the current Medtronic system’s values and shortcomings.
 
I recently updated my insulin pump from an old Animas pump (IR1000) to a Medtronic 722 Real-Time for just this reason: Medtronic, uniquely, has incorporated the display for their CGM system into their insulin pump. In this way one unit serves two purposes, alleviating the need to carry a separate device. 
 
You get constant and frequent bg feedback – every 5 minutes, 24/7, approximately 280 readings/day.   In addition to your bg values (in mg/dl or mmols) it also displays a graph which shows you at a glance whether that number is rising, falling or level, a critical piece of information as we all know. It also tells you whether you are rising or falling precipitously with either one or two arrows pointing up or down. This trend information is probably its greatest strength. Knowing my bg is 85 mg/dl (4.7 mmols) is usually pretty good news… unless I happen to know I’m plummeting, at which point I need to eat something fast. You can also pre-set high and low bg levels where you’d like to be alerted. I have my high set at 200 mg/dl (11.1 mmols) and my low at 65 mg/dl (3.6 mmols). Whenever the sensor says I’ve dropped below or above these numbers it warns me with a beep or vibration (or I can turn it off). This can be handy at night for obvious reasons. 
 
I’m also going though considerably less test strips. During the first week or two I was probably using more strips than usual, as I couldn’t resist the temptation to constantly test and compare numbers. You do in fact have to calibrate the system with meter tests 2-4 times/day to keep its accuracy in check. Because you can look at either a 3-hour or 24-hour graph, it’s a great tool for tweaking your basal rates, particularly nighttime basals which you don’t normally see. 
 
I’ve found it to be a godsend when skiing on some very cold Montana days – you can actually check your bg without even taking off a glove! And you can easily check every 15 or 20 minutes to see how that lunch bolus worked out, when it peaked or whether you need more insulin. Plus, since the sensor is literally in your body (subcutaneous), it’s always warm and entirely unaffected by the cold. You just look at the display (your pump) and read the number. On the 4 days I’ve skied with it, unless I have reason to not trust the results, I don’t even bother doing a finger-stick. I’ll wait and do a “meter test” when I’m inside, my meter is warm and completely reliable and enter that value for a calibration. 
 
But it’s not perfect. Since you’re actually testing interstitial fluid and not blood directly, there’s a 15-20 minute delay from “real time” blood values (meter results) to sensor values. If your bg isn’t rising or dropping quickly it’s a non-issue. But if it is – as indicated by the sensor – you have to mentally take that into account. For instance, if the sensor reading is 150 mg/dl (8.3 mmols) with the graph ascending and showing 2 up-arrows, I’m probably more like 180-200. And speaking of accuracy, you need to learn when the values are accurate and trustworthy and when they’re not. It’s largely a matter of knowing when to calibrate and how often, something that takes a little figuring out. 
 
Then there’s the cost. At this point in the dark ages of diabetes, most insurance companies aren’t covering it. Mine finally is but it took some convincing. Otherwise the cost for the sensor/transmitter system plus 10 sensors is a whopping $1000 USD. The sensors themselves are $35/each and are only “certified” to be used for 3 days. Absurdly expensive!  But there are ways to extend the life of the sensors to make them affordable. Of the 4 sensors I’ve used, the shortest I’ve worn one is 5 days. The longest was 14 days. The amazing thing (to you pumpers out there) is they produce virtually no skin irritation compared to an infusion set. Since they don’t introduce anything under the skin, they’re apparently tolerated much better.  
 
Another down side is you end up wearing yet another subcutaneous “probe.” As a pumper for 8 years, I’d gotten used to one always being there. Now there are two. You also develop a fascination with micro-managing your bg with all this new data. You tend to check the display on your pump every 10 minutes like a teenager checking their damn cell phone. (I now wear my pump on a clip where I can check it easily rather than in my pocket). You also have the alerts – low bg, high bg, calibration reminders. Fortunately, they’re easily turned off if you’re aware of the situation and tired of being reminded your bg is high. If you don’t want the data, it can be information overload.  But I love it. 
 
Two things I’ve learned so far: 
·        To minimize or even eliminate the classic post-prandial rise in bg, do the obvious – bolus 15 minutes before eating. This is something I’ve always suspected but it’s nice to see it supported with the results visibly graphed out in front of me. During my sedentary work day, this is possible, in the mountains, it’s much easier said than done.
·        I’ve concluded that splitting your bolus is what your body secretly does all the time! Medtronic calls it a “Dual Wave Bolus,” Animas calls it a “Combo Bolus.” Regardless, it’s when you deliver some of your bolus immediately and the rest of it spread out over a certain amount of time. I now do this for 80% of my food boluses. With the delay in metabolism from meals with any significant fat component, it seems to cover the real carb load much better than one single blast at mealtime. Verifying this is where the CGM comes in handy. You can do a meter test 2 or 3 hours after eating but you’re still only getting snapshots. The CGM gives you a much fuller picture. 
 
Sorry for the long ramble. Any questions – please add a comment.
Jeff