Continuous Glucose Monitor (CGM): The Pros & Cons
CGM is a great tool for you to consider adding to your family’s diabetes tool kit, but like all tools, it lightens some burdens and adds others. Here we outline the benefits and drawbacks of using a Continuous Glucose Monitor, so you can consider these factors in terms of your family’s needs and preferences, and decide for yourself if this tech tool is a good match for you.
Before you read on, take a moment and ask yourself: why do I want a CGM? What are my deal-breakers, the things that I can’t stand to live with, or live without? Then see how your family’s priorities and values fit with the information that follows on the pros and cons of Continuous Glucose Monitoring.
What Value Does CGM Add to My Life?
Monitoring your glucose continuously provides invaluable information that you can’t (easily) get any other way... Like how quickly blood sugar rises when your 9-year-old has a big bowl of cheerios. And how long of a pre-bolus do you need before you eat in order to flatten out those post-meal spikes? (15 minutes? 30 minutes? More?) How does that necessary pre-bolus time vary for mashed potatoes versus brown rice? And when should I start an extended bolus for fat after I eat pizza? (1 hour? 2 hours? more) What’s going on in the middle of the night that results in a wake-up BG of 14.8... does BG steadily climb across all 10 hours, or is it stable and in-range all night until it spikes right before wakeup? And (perhaps most importantly for our family, since our son doesn’t reliably detect his lows)...
Am I headed for a low BG, even when I don’t feel it coming?
The Benefits of CGM:
CGM provides more than just a static number, it also provides glucose trend information (in real-time), which tells you not just where your glucose is but also where it’s headed. 5.5 and headed straight down is very different from 5.5 and rising. With this glucose trend information, you’re in a better position to make an informed choice about what to do about your current glucose level: take in extra carbs? Give an extra dose of insulin? Do nothing?
Trend information can also help you with managing diabetes around physical activity. You will likely take different action if your glucose is 5.5 and steady right before you exercise, than if it was 5.5 and rising right before you exercise.
Tip from the Trenches
Trend information has been the greatest advantage of CGM for our family, and has definitely helped reduce glucose swings for our school-age son. Instead of just having a static number, and wondering “will his sugar go low if he doesn’t eat right now?” or “does he need an extra snack right now or can it wait until he’s hungry?”... with trending information we have extra information to inform that decision. If his glucose is 6.0 with “double arrows down”, I know he needs to eat something with fast-acting carbs to avoid a low. But if his glucose is 6.0 and steady, or 6.0 and rising, then he can wait to eat when he’s hungry, like kids without diabetes can choose to do. This freedom has been invaluable to our family. In a similar way, the trends inform our decisions about dosing insulin for regular meals and snacks... if the trend arrows tell us his glucose is rising before lunch, we may bump up the I:C ratio so that he gets more insulin for the meal than usual. This has helped prevent some highs that might have otherwise occurred if he received the usual insulin dose. The same is true in the opposite direction; we may give less insulin for the meal if his glucose is trending downward. Being able to rein in many of these highs and lows has had a huge impact on how our son feels, physically and emotionally... highs and lows feel crappy!) – and THAT, above all else, makes CGM worth it to us.
CGM measures your glucose levels continuously, without you having to tell it to, at times when you’re thinking about everything besides diabetes. So that means it detects highs and lows that you may have otherwise missed, and notifies you with programmable, attention-getting alerts. This is especially important for young children, who may not reliably detect their lows, or may not communicate their lows to parents so we can help them.
CGM can even help you catch some lows before they happen. Predictive alerts (such as “Alert Before Low” and "Urgent Low Soon Alert") give you a heads-up that a low may be imminent, so you can take action to before you get there. The same is true of highs: there is a High Glucose Alert, which gives you the opportunity to get a dose of correction insulin in earlier than you may have otherwise noticed.)
This can have a bonus side-effect in terms of the emotional burden of diabetes: some users report that having this “safety net” reduces their anxiety about low blood sugar.
Tip from the Trenches
CGM warns when you’re on the verge of a low or high, so you can intervene sooner, and even avoid a low or serious low. Our son gets symptomatic less now that he uses CGM, we are catching many of the lows earlier, and so are treating before he gets dizzy, shaky, and emotional. Often it warns us of a low before we see any symptoms, which allows us to treat the low sooner, so his recovery from lows is easier.
- Jacky H., Diabetes-Mom
The very first time we used CGM for our then-4-year-old son (during a CGM trial) we inserted the sensor, turned on the receiver and then headed to Toys R Us a few hours later. We had just had lunch, so we never would have thought to check his BG at that time, especially during the fun of the toy-frenzy. But when the low alert went off in the store, we checked BG by doing a fingerstick, and sure enough, his BG was low. We were able to treat the low and move on with minimal interruption! ~Michelle
3. View Glucose from a Distance
Today’s CGM systems can send the data from the transmitter (on the CGM-wearer) to a receiver that is several feet away. Additionally, with remote-viewing the data can then be picked up and viewed from any other (connected) location in the world!
For starters, this simplifies the middle-of-the-night glucose checks for parents who do so – now instead of getting up to do a fingerstick BG meter check, parents can keep a receiver on their night-stand, or can remotely view the CGM data on their smartphone... one peek at the display lets you know if further action is needed. If not, you can simply close your eyes and go back to sleep.
Tip from the Trenches
This one was huge for us! With a communication range of 6 metres, our night stand is close enough to our son’s bed that we can place the CGM receiver there while we all sleep. On nights that we have reason to check his glucose level during the night, when the alarm clock rings we simply glance at the receiver display. If glucose is too high or too low, we still have to get up to deal with it, but if things look good, we’re back to sleep in moments. ~Michelle
4. Pattern Detection
Since CGM measures your glucose levels between fingersticks, this gives you enough historical data points to track patterns in glucose. The CGM receiver also gives you a visual representation (line graph) to make those patterns clearer. The helps with assessing the effectiveness of your current insulin doses, both basal and bolus, as well as the effect of food and exercise on glucose levels.
Assessing overnight basal doses becomes clear and easy when you can see a line representing glucose levels overnight, because you know exactly when glucose is rising (and therefore an increase in basal insulin for that time period may be needed) and when glucose is falling (and so a reduction in basal insulin may be needed in that time period). In much the same way, seeing that line rise or fall after a meal tells you lots about the effect of different foods on glucose levels, how quickly some foods affect blood sugar, and how well the current insulin dose is working. If you often see steep lines after lunch, that may mean more insulin is needed for food at that time. If you see glucose drop after eating supper, that may tell you that too much insulin is being given for the evening meal. With this information, you’re in a better position to recognize trends and then to adjust insulin to even out future high and lows.
Tip from the Trenches
This was certainly the case for our family! We didn’t see much of a difference in BG swings when our son started on a pump at 3 years old, but when he got his first Dexcom CGM at 4 years old, we saw big drop in the swings. I could see clearly that overnight his BG just kept rising, so I had confidence to turn up his night-time basal rates; before that I worried that the wakeup highs were caused by a rebound from overnight lows that we were missing. As another example, I could clearly see a flatter curve in the trace when we made sure he got a solid 15-minute pre-bolus compared to other times when we skipped the pre-bolus (huge post-meal spike).
Further, as a result of reducing the BG swings, our son’s A1C dropped at the first assessment after starting CGM... a meaningful benefit of using CGM, since reducing A1C decreases the risk of future diabetes-related health problems. ~Michelle
5. Not the Granny Panties of Diabetes Devices
Though much has been said about the hassle of carrying another device, and the bulky, utilitarian nature of some diabetes tech devices, today’s CGM devices are actually relatively discreet, unobtrusive, and (dare I say?) stylish. Some CGM systems are integrated into an insulin pump (two devices for the carrying load of one!). Others give you the option of using your smartphone to receive and display your glucose data, so to the outside world you look like you’re texting, just like everyone else!
Why might I NOT want a CGM at this time?
Despite all the benefits of CGM discussed above, a given piece of diabetes technology is not necessarily a good fit for everyone, and CGM is no exception. As with all technology, it has its drawbacks and there are reasons why some individuals with diabetes may choose not to add this tool, or may choose to add it intermittently to their diabetes tool kit. Even for those people for whom the benefits outweigh the drawbacks, there are important considerations to keep in mind as you use CGM, in order to stay safe and healthy.
The Limitations of CGM:
1. Tech Burden
Some CGM users report feeling that CGM is one more device to wear, one more thing to learn, one more set of alarms to attend to and sensor changes to remember. You will have to assess for yourself whether the burden of diabetes that is lifted by using CGM outweighs the burden of the extra tech piece.
2. Data Overload
Continuous monitoring produces lots of data. I mean, LOTS of data. Sometimes it feels like too many numbers to know what to with them. CGM trainers suggest spending the first week on CGM just watching the output without making changes; look at broad trends rather than dwelling on specific numbers; avoid the temptation to peek at the display too often. In short, to use CGM effectively without it threatening your sanity, you need to be able to put it in its place.
3. CGM is not fail-proof
...so it’s unwise to “set it and forget it”. There can be periods when the system is “down” or the reading is not accurate. In one manufacturer’s educational materials it states: “In a pediatric clinical study a significant number of low glucose events were not detected by CGM. Do not rely solely on CGM alerts to detect low glucose.”
Therefore, while using CGM it’s important to continue all the other “best practices” that keep you safe and healthy (symptoms of high and low glucose should not be ignored just because the CGM reading says glucose is in range; do regular fingerstick BG checks if your sensor glucose readings do not fit with your symptoms, and to calibrate the sensor); if you have reason to be concerned about a night-time low, still set an alarm to check that night, even if it’s just to check that the CGM is still operational and the reading is in-range.
Tip from the Trenches
There have been times when our son’s CGM reading said that his glucose was in range, or even above range, but he was clearly experiencing hypoglycemia (his traditional BG monitor said 3.3, he felt dizzy and very hungry). Although it’s accurate the majority of the time, and although I know other people who find their CGM consistently reads within one point (mmol/L) of a fingerstick result, in our family we have had too many inaccuracies and missed lows to trust the system entirely. (That does not, however, undermine the real value we find in the trend information and in the detection of lows when it is accurate.) Also, since we've been using the Dexcom G6, we've found much greater accuracy, and our trust in the sensor has grown immensely! ~Michelle
4. Tech Frustration
The periodic inaccuracy can create additional frustrations that don’t occur with fingerstick testing. Those same alarms that are so valuable when they catch an undetected low are equally frustrating when they go off for a false low. Especially in the middle of the night. And there’s nothing more maddening than 2 hours of a display that reads only “???”.
Tip from the Trenches
Small children and those with a lean body type may be more prone to sensor mix-ups, since sensors read glucose best when bathed in interstitial fluid, not bumping up against muscle. Our sleep quality is usually worse when our son wears his CGM, as it often wakes us up in the middle of the night saying his glucose is low, but when we check with a fingerstick and conventional BG meter, it often reads a beautiful 5.3, or similar. We would prefer to sleep through in-target blood sugars! It’s important to note, however, that this issue (likely due to Pressure Induced Sensor Attenuation (PISA); that is, pressure on his sensor when he lays directly on it as he sleeps, which creates a false low reading) is greatly affected by site location and other factors. -Michelle
5. Sites Take Up Surface Area
A sensor occupies space on the body, and for some people (especially small children, and insulin pumpers) there’s just not enough real estate to meet the demand.
Tip from the Trenches
Because our son is young and wears a pump, we need to balance the need for pump infusion sites with the need for CGM sensor sites. That fact that he has quite a lean body type means that there are fewer potential areas for both. Because of this, we choose to use the pump full-time and the CGM part-time. ~Michelle
6. Financial Cost
There is an up-front financial cost for any CGM system, as well as ongoing material costs (for sensors, transmitters, and more occasionally, receivers). Although some provincial programs cover the cost of insulin pumps and supplies, I haven’t heard of one that covers the cost of CGM. Many families that I have spoken with don’t even have CGM coverage under extended health insurance plans (although it is possible to appeal if you do not have coverage under your private/employer health plan – sometimes with a letter of necessity from your child’s doctor, health insurers may choose to cover CGM supplies in your individual case).
7. Pain or Discomfort
Inserting a sensor requires another “poke”, which may involve some degree of discomfort or even pain. This depends on individual tolerance, age of the user (kids may be more sensitive to and anxious about pain), the type of sensor, and site selection. Some people report that they barely feel it when they insert a sensor; others say that some insertions sting quite a bit. If you’re concerned about comfort of insertion, talk to others in the T1D community who have used CGM to get their impressions of the different systems; check into the gauge (thickness) of the introducer needle in the system you are interested in – a larger number means a smaller needle, and therefore less discomfort during insertion. You can also use numbing cream to make sensor insertion more comfortable.
8. Skin Reactions
Negative skin reactions including rash, itching and irritation are a reality for more than a few people. It seems that some bodies have problem with the adhesive tape around the sensor pod; less frequently the problem is the sensor itself. If this is an issue for your T1D child, check out Waltzing the Dragon's article: 15 Solutions to Reduce Irritation and Keep Sets & Sensors Stuck On
9. Can’t Always Say Good-bye to Fingersticks
CGM doesn’t entirely replace fingerstick blood glucose checks. Some CGM systems require a fingerstick check with a BG meter to confirm the CGM reading before dosing insulin or treating a low. It’s notable that the Dexcom G6 and Libre 2 systems have been approved to replace fingerstick checks for insulin dosing and treating lows, and does NOT require calibration fingerstick checks either. However, fingerstick BG checks are still needed for all systems when your symptoms don't match the CGM readings, or when the system is missing critical information (both a number AND a trend arrow are needed - if either one is missing, Dexcom recommends acting on the results of a fingerstick BG check instead of the sensor reading). So if you want to wear a CGM so you never have to poke your finger again, you’ll be disappointed. (Although use of a CGM can GREATLY reduce the number of pokes needed in a day.)
Tip from the Trenches
When my daughter wears CGM it may save a poke or two on the ski hill if, for example, the trend shows her BG as steady and in-target, or slowing dropping at just above target. It would give you a ballpark idea so you'd know if you need to verify with a finger poke. ~Heather M., D-Mom
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