Sheri Colberg, PhD
My Love-Hate Relationship with CGM
I currently have a Dexcom G6 continuous glucose monitoring (CGM) device, and I have to say that I both love and hate it. Why, you ask? It’s complicated.
Nowadays, it is increasingly common for people with type 1 diabetes to have CGMs, such as the latest ones from Dexcom, Medtronic, and Senseonics, or intermittent ones like Abbott Freestyle Libres that have to be scanned to give the glucose reading. To keep it simple, they are all generally referred to as “CGM.”
If you’re new to diabetes or have only had it for less than a decade, you may have started out with a CGM to monitor your glucose levels and never question using one. You need to know what your glucose level is, right? My path to CGM has been vastly different, which may at least partially explain my love-hate affair with using one.
I started out with urine testing in 1968 when I was diagnosed with type 1 diabetes at age 4. Some of my earliest memories are putting 5 drops of urine and 10 drops of water into a test tube, followed by a tablet that bubbled up to a color ranging from blue (no sugar) to bright orange (lots of sugar). I remember having a lot of orange test tubes, which always made me feel guilty. This method was all we had back then. Unfortunately, it could only tell you that your blood glucose had been high enough at some point (~200 mg/dL) for excess sugar to spill over into your urine, but not a thing about your actual, real-time glucose level.
In 1986, after having lived with diabetes for 18 years using only how I felt as my glucose guide, I got my first fingerstick blood glucose meter. What a revelation that was! By sticking my fingertips multiple times daily with a device that looked and worked like a mini-guillotine, I was able to start adjusting my insulin doses and timing of meals for the first time ever—whereas before I had to eat to feed my insulin, which had always been the same doses given at the same times. I also found out that blood glucose levels are not that easy to manage, even when you do everything the same two days in a row.
Since then, I have always appreciated being able to find out what my blood glucose is, though, especially after only having urine testing for so many years. Back in the 1990s, my insurance would only cover 4 glucose checks per day, which is woefully inadequate for most people with type 1 diabetes. I remember fighting to get them to cover 8 when I was pregnant the first time but, thankfully, now I can get almost unlimited strips for not much copay.
Back in the early 2000s, I actually did a research study on the first CGM that was approved, a non-invasive monitor called the GlucoWatch. The fact that you have probably never heard of it tells you all you need to know about how well it worked (hint: it didn’t most of the time). The device was worn on your wrist like a watch, pulled fluid out of your skin, and tested it for glucose—and left angry red marks on my skin wherever I wore it. It also shut off whenever I sweated under it, even a little bit, which happened all the time whether I exercised indoors or outdoors or just sat outdoors when it was the least bit warm.
When the first version of the Dexcom CGM came out, I tried that as well, but it was so frustrating that I gave up using it after 3 weeks and put it in the back of my closet. Half the sensors I could never get to calibrate, and the rest either died early or were horribly inaccurate. It also had a probe under the skin that did the monitoring, so it was considered an invasive device. Since then I also tried the Dexcom G5 several times, the Freestyle Libre 2, and the Dexcom G6 devices.
In short, I have loved and hated every CGM device I have ever tried. What follows is a compilation that explains why my relationship with them is so complicated.
What I love about CGM:
Getting a glucose reading every five minutes
Being able to see patterns and trends of my glucose levels
Being able to check my glucose on my CGM at night without having to wake up fully
Being able to read my glucose levels in the dark on my phone
Not having to stick my fingers (although I really don’t mind sticking them that much)
What I hate about CGM:
Getting a glucose reading every five minutes (especially time-delayed)
Lag between my blood glucose and CGM glucose levels (typically 6 to 20 minutes)
How inaccurate the glucose readings are at times, especially the first 24 hours of a new sensor (see picture) and sometimes the last few days before it hits its lifespan
How often I end up checking my blood glucose on my meter anyway (since I don’t believe the CGM is right—and it often is not)
Mental stress that arises from the alarms and over treating my highs (due to time lag)
Not being able to turn off all the alarms (low alarms on a Dexcom are non-negotiable)
The limited number of places to wear a sensor without it getting in the way or being in a spot that gets irritated (by clothing, lying on it, etc.)
Compression “lows” from lying on the sensor or wearing tight clothing
When its inaccuracies mess up my “time in range” values
Having to carry my phone around with me everywhere I go (even to the next room) so it won't lose its signal
Not being able to adjust the placement of a sensor after I put it on (and find out it's not in the best spot for myriad possible reasons)
Having something on my body that often itches or hurts (and reminds me I have diabetes)
Cost of using it—even with insurance, my copay is close to $100 a month
Dexcom customer support (and waiting hours to talk with a rep)
The fact that the Dexcom transmitters have an expiration date (I have had one expire before I could use it when taking a break) and that they only last 90 days from first use (although the upcoming G7 will have an integrated transmitter as part of each new sensor)
After years of inaccurate urine testing, above all I have come to expect and demand accuracy with glucose testing. I do realize that blood glucose meters are inaccurate at times, but more often than not, my fingerstick values match my symptoms (of lows and highs). I find this to be true less often with my CGM glucose readings, likely due to the time delay and other items mentioned.
I always experience a mental health boost whenever I take a break from my CGM (and I do this quite often). However, I will never ever give up using a blood glucose meter at this point—it does help to know what my glucose is doing in real time. For me personally, my A1C is equally as good whether I check my blood glucose with a fingerstick 10+ times a day or wear a CGM and get 288 glucose readings a day. If you want to try other options, don’t hold yourself back. Whatever approach works for you, stick with it. That’s what I am doing.