More Thoughts on My New CGM

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More Thoughts on My New CGM

I’m in the middle of my fourth day using my continuous glucose monitor (CGM), and I can say a few things rather definitively:

1. I will NEVER go without a CGM again, as long as I can possibly help it.

2. This thing has a bit of a learning curve.

3. As long as its limitations are understood, it is one of the most valuable tools someone with diabetes could ever ask for!

OK, so I’m clearly a fan. Only a few days in, and I’ve already adjusted my morning long-acting insulin to achieve better results than I’ve seen in a long time — the graph throughout my day stays right in the sweet spot, not rising and not falling (well, falling a little with exercise, rising a little with severe stress, but you get the idea — these fluctuations are always with us, and very manageable, but the overall trend is so pleasingly stable!). My overnight readings give me a perspective I’ve simply NEVER had, and will allow me to tailor my overnight long-acting insulin in a way I’ve never been able to before.

The CGM has been equally useful in understanding my meal-time insulin. I can see timing errors — that is, I can see if the spike of my insulin is off from the spike that comes with what I eat. I can get a much better sense of WHEN I should inject that short-acting insulin so that spikes match up. I can see severity of the rise in glucose, and exactly how effective my ratios are. These, too, have been adjusted after only a few days, and are yielding much better, more stable, and “in-range” results.

So yes, I never want to be without this tool again; but it’s not perfect. As I mentioned in the first part of this series, the CGM does not actually measure the glucose in your blood. It measures the glucose in your interstitial fluid (the fluid between cells), and this reading lags behind your blood glucose by about 10–15 minutes. That means that what I’m seeing on my CGM is not my current number, but the number I was 10–15 minutes ago. Now, if the last 30 minutes of readings have all hovered around the same number, then the number I’m seeing is probably within a few points of the number my blood glucose actually IS (I checked just now, in fact — I’ve been in basically a straight line for the past 30 minutes, and the numbers were an identical 108). But if that blood glucose is rising or falling, it’s a different story.

Dealing with this lag time is actually easier than it sounds, though. Let’s imagine a graph with a curve moving gradually downward at the end in a relatively straight line. Assuming the monitor is reading, say, 95, I can rest assured that my actual number isn’t going to be any lower than 85. Why 85? Because that line is moving down, and that 95 isn’t what I am NOW — it’s what I WAS 10–15 minutes ago. But it wasn’t moving steeply down, so the odds that I’m in any range of being dangerously low are very slim. But let’s say I just got done exercising, and that number wasn’t a 95, but a 71. And let’s say the line is moving down more severely. Well, then it’s time to get out the old OneTouch and do a finger stick. That’s because if I am moving down quickly, and I was 71 ten minutes ago, I might be around 58 by now!

It’s also very helpful to see the shape of the line. If I see a curve was moving down, but leveling out, I know two things. First, I know that I’m not in emergency territory (assuming, of course, that the CGM isn’t reading something like 60). And second, I can use my conventional meter to give me MORE information on where I’m trending. If my CGM is telling me the following:

131, 120, 108, 100, 96, 93…

And my finger stick tells me:


I can be pretty certain that the downward trend leveled out, because I WAS 93 ten minutes ago, and I AM 95 now. Using the two sources of information gives me a FAR more accurate and detailed understanding of what that conventional meter reading of 95 means.

As I mentioned in the beginning, the CGM isn’t perfect. These lag times are a definite limitation of the CGM, and it really is true that the CGM can’t replace your traditional meter. But when the two are used in tandem, it is rather remarkable what a complete picture you can get of what your body is doing throughout the day. And as long as that graph on the CGM is moving gently (that is, moving up or down slowly), the CGM CAN help you avoid severe lows and highs by showing you exactly how your glucose is trending! To give you one last example, the other day I saw this on my CGM while teaching a lesson (a time when a traditional finger stick isn’t really a possibilty):

97, 91, 85, 80…

Now, 80 is a number that sits perfectly in range. But that downward trend told me that the true number was closer to 70. AND that graph was moving solidly down, not leveling out. So, in spite of the manufacturer warnings not to make treatment decisions with the CGM, I went ahead and took 15 grams of sugar. I didn’t take enough to shoot me severely high, but enough that I would head off a severe low. Then between lessons I could check with my regular meter to confirm that yes, I was trending low, and yes, the 15 grams of sugar was sufficient to bring me back in range. Without the CGM, I would have been at the mercy of my own sensations of feeling low, and I would have responded AFTER I had already plunged below 60 (most likely), causing a disruptive down-and-back-up swing in my numbers, and possibly interfering with my ability to concentrate during the lesson, affecting not only MY sense of well-being, but the quality of the product I was offering my student!

Tune in next week…

Well, that’s all for today. Tune in next week for my final entry on the CGM experience. In addition to wrapping up my own experiences with this technology, I’ll share some comments excerpted from an interesting interview I read with Kevin Sayer, the CEO of Dexcom. He gives some fascinating insights into where the technology stands currently, where it’s going in the future, and what kind of work is being done behind the scenes to increase the accessibility and affordability of this technology for more people.

Women who conceive in the winter are at higher risk of developing gestational diabetes, according to new research from the University of Adelaide. Bookmark and tune in tomorrow to learn more.

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