CGM vs Libre: Which is Better?

Choosing Your Best Glucose Monitoring System: what’s available in Canada? what features should I consider?

Michelle MacPhee
Diabetes Mom, Creator/Co-Founder of Waltzing the Dragon

Many tech options have been added over the past several years that add value to the way we self-manage diabetes. However, the increase in options has also led to an increase in complexity that can easily become overwhelming. I hope to simplify things here by outlining the different glucose monitoring options that are available here in Canada, along with the relative pros and cons of each option, so that you can choose a technology that best fits your needs.

But let’s start with the basics by clarifying what is meant by “Glucose Monitoring” technologies…

For decades, individuals with diabetes (type 1, type 2, gestational, etc) have measured the amount of sugar (glucose) in their body by applying a drop of blood to a glucose-sensing test strip inserted into a glucose meter. This “fingerstick” method measures the concentration of glucose in the blood, which can be compared to recommended blood glucose targets and so guide our treatment decisions to optimize our diabetes self-management. Fingerstick measures capture your glucose levels at a single moment in time, much like a snap shot. More recently, however, methods for monitoring the amount of glucose in the body have been developed which provide a broader view of where your glucose levels are, where they’ve been and where they’re going. These methods provide more of a movie than a snap shot. They include Continuous Glucose Monitoring and its younger cousin, Flash Glucose Monitoring.

What are CGM & Flash?

Continuous Glucose Monitoring (CGM) devices (such as those offered by Dexcom and Medtronic) use a sensor (a fine electrode inserted just underneath the skin and held in place by an adhesive patch) to measure and report the current level of sugar (glucose) in the body. Each sensor remains in place for about a week. This is a do-it-yourself process, you don’t need a medical professional to insert the sensor: the user applies the sensor with the push of a button using an automatic insertion device (sometimes called a serter). Unlike traditional fingerstick methods, which measure glucose levels in the blood, CGM measures glucose levels in the fluid surrounding the cells (interstitial fluid). These glucose readings are sent from the “transmitter” (attached to the sensor) to a “receiver” which displays the current glucose level, as well as the glucose trends (that is, whether glucose levels are steady, increasing, or decreasing) so that you can take action as needed. These glucose readings are taken continuously by the system, without user input after insertion, so that a complete glucose history (in the form of a graph, or “trace”) is available to the user at any time.

In addition, because the system is continuously monitoring glucose levels, it can notify you (via “Alerts”) when those levels approach or cross low (or high) blood sugar thresholds that you have set. Flash Glucose Monitoring (that is, Abbott’s Freestyle Libre, the only Flash system currently available) works in much the same way as Continuous Glucose Monitoring, however, the glucose readings are transmitted from the sensor only when the sensor is scanned by waving the “reader” (i.e receiver) over the sensor. The original Libre system does not have these alerts, BUT Freestyle's newest system, Libre 2, does have  independent alerts, even between the times that you scan the sensor.

Both Flash and Continuous Glucose Monitoring technologies have been developed to replace fingerstick BG checks; the different systems accomplish this goal to varying degrees.

There are three companies currently providing CGM and Flash systems in Canada:

  • Abbott offers the Freestyle Libre and Libre 2 (Flash Glucose Monitoring systems)
  • Dexcom offers the G6 Continuous Glucose Monitoring (CGM) System
  • Medtronic offers the Minimed 630G/670G/770G (Integrated Insulin Pump + CGM Systems), as well the Guardian Connect (stand-alone CGM system)

For a side-by-side comparison of the systems available in Canada:

How Do I Find the Best Glucose Monitoring System?

There is no such thing as a universal “best” choice; the best choice for you is the device that most closely fits your needs, preferences, and budget.

With this in mind, a good place to start is by asking yourself:

  • What is it about my current diabetes care routine that feels most burdensome?

  • What diabetes care problem would I most like to solve?

  • What do I want from glucose monitoring technology?

  • What is the out-of-pocket cost of a given system and can I afford that (or is it covered by my insurance)?

For some people, it’s the demands of frequent BG checks that wear them out. For others it’s the anxiety of being alone and not recognizing a low BG. For others, it’s worry about a loved one, such as a partner/spouse, child, relative or friend. Still others want a full picture of their glucose patterns so that they can adjust insulin doses to reduce glucose highs and lows.

There are many things to think about when considering Continuous or Flash Glucose Monitoring…

What are the benefits of CGM & Flash?

All of the above systems (Dexcom G6, Medtronic, and Libre/Libre 2) provide a number of benefits:

  • All three systems replace many of the pokes demanded by the more traditional fingerstick blood glucose (BG) meters (although all three systems still require a “poke” in order to insert the sensor).

  • All three systems provide glucose trend information to tell you in the moment whether your glucose is steady, falling, or rising, and how quickly.

  • CGM and Libre 2 provide Glucose Alerts. That is, the system will notify you when your glucose is low (which is especially valuable for people who don’t reliably recognize lows), as well as when your glucose is above your target range (which allows you to take corrective action earlier). In addition, Rate of Change Alerts notify you if your blood sugar is dropping or rising quickly. Alerts provide safety and peace of mind for individuals living with diabetes and their families.

  • All three systems provide historical glucose data that you can look back on to analyze glucose patterns across days and activities, answering questions like: is there a time of day that my glucose tends to be high (and therefore I may need more insulin at that time)? Is there a time of day or an activity that tends to increase my risk of low blood sugar (and therefore I need to adjust insulin, or account for the glucose demands of exercise)?

  • All three systems back-fill “missed” glucose data if the system components have been out of the communication range for a period of time.

  • All three systems provide reasonable accuracy (have been approved by Health Canada as such), within the same ball park of accuracy that we currently get with blood glucose meters.

(For details on accuracy and a comparison of the three systems, see the CGM/Flash Comparison Chart.)

What are the potential drawbacks of CGM & Flash?

It’s also important to keep in mind the potential downsides to all three glucose monitoring systems, in case any are deal-breakers for you:

  • Financial Cost: All three systems involve a start-up cost, as well as the ongoing cost of disposable supplies, which can be higher than the cost of fingerstick blood glucose monitoring. The start-up cost of Flash systems (Libre) is the lowest, and the ongoing costs also tend to be lower than those of CGM.

  • Because of the adhesive patch that holds the sensor in place, as well as the plastic of the sensor housing, all three systems pose a risk of minor or serious skin reactions.

  • None of the systems replace fingersticks entirely, although Dexcom’s G6 replaces most fingersticks… you don’t need fingersticks to calibrate it, nor to give a correction for high BG, or a treatment for low BG (unless the system is missing critical information, or if your symptoms don’t match the sensor reading).

  • All involve a small lag-time between blood glucose readings (obtained by fingerstick) and interstitial fluid glucose readings (obtained by CGM and Flash).

  • The flip-side of the benefit of CGM Alerts is that sometimes there are false alerts which can occur at any time. Including 2am. And at any time, those bings and tones can be a nuisance.

  • All of these glucose monitoring systems can involve some degree of information overload… sometimes it can be overwhelming to know what to do with all those data points, trends and patterns; it involves (sometimes serious) work to sort through it all in order to get full benefit from the technology.

What Key Features Should I Consider?

In addition to the above, certain systems carry unique benefits not shared by all others. You may want to consider these key features when choosing a glucose monitoring system:

  • Do you want your glucose monitoring system to give you a “heads up” when your glucose is low, high or changing quickly? Glucose Alerts are provided by CGM and Libre 2 (not the original Libre system). Also ask yourself: Which alerts are important to me? Do the alerts and their variable settings fit my family’s needs? Can the thresholds be set high enough and low enough to give me the information I’m looking for?

  • Do you want a separate alert for when a low is predicted (Alert Before Low) PLUS an alert for when you’re actually low (Low Alert)? Take a closer look at Medtronic or Dexcom.

  • How often are you able and willing to insert a new sensor? Sensor life on the 3 systems varies from 7 to 10 to 14 days (for Medtronic, Dexcom and Libre, respectively).

  • If reducing finger pokes is a top priority for you, then you may want to focus on a system that is approved to replace fingerstick glucose checks for treating lows and correcting highs, and that does not require calibrations (Dexcom G6 and Libre 2).

  • Do you crave simplicity? If you’re looking for a straightforward replacement for fingersticks, Libre offers an easy-to-learn system, without the nuisance alerts that come with CGM.

  • Integrated or Stand-alone? In an integrated pump/CGM system, the CGM reading displays on the face of the insulin pump, which means the two components communicate with each other, and you have one less device to carry. With a stand-alone system, the receiver is separate from the pump, which means you have to carry one more device, but it also gives a parent the option of keeping the receiver on them, even if the child some distance away. Dexcom and Medtronic offer integrated systems.

  • Do you inject your insulin and want to stay that way? A stand-alone system allows those on injected insulin programs to use CGM for monitoring glucose levels and trends, without having to use a pump for insulin delivery. All three manufacturers offer stand-alone systems: Medtronic Guardian Connect, Dexcom G6 stand-alone, and Freestyle Libre/Libre 2.

  • Do you want your basal insulin to be shut off temporarily when your glucose is low and you don’t respond to the alert (such during sleep or during a severe low)? If so, Medtronic’s integrated pump+CGM system offers a Low Glucose Suspend; Dexcom integrated with t:slim offers the same function with either Basal-IQ or Control-IQ software.

  • How important is accuracy to you? The value of a CGM system is depends on how much you can trust the information it’s giving you; the more accurate a sensor is, the more you can trust it. Greater accuracy also improves the frustration factor, as it reduces the number of false alarms. Alerts are only a hassle if they are false alarms; if they alert you to a real high or low, then they’re a gift, not a hassle! If you’re looking for the most accurate system available in Canada right now, that’s Dexcom.

  • The transmitter-to-receiver communication range (distance that the transmitter can be from the receiver and still work) varies between the different systems: for Libre, you need to be within 4 cm (which means you’re still getting out of bed for middle-of-the-night glucose checks); the range for the Medtronic CGM is 2 metres; Dexcom’s range is 6 metres. If it’s important for you to view the CGM-wearer’s glucose reading and trend without having to be right next to them (such as when your child is playing in another room, or when you want the receiver at your bedside while your T1D child sleeps in their room), you may prefer a CGM system with a long transmitter-to-receiver communication range OR one with remote viewing of data.

  • Do you anticipate frequent or long interruptions in communication between the sensor/transmitter and receiver? If you’re a transatlantic business traveler (so put your system in airplane mode for many hours on a flight) or a swimmer who spends many hours in the pool (and so leave the receiver at the side of the pool for prolonged periods), you may find value in longer data back-fill options offered by Libre and Medtronic (the transmitter on the Libre/Libre 2 stores 8 hours of glucose data between scans; Medtronic stores 10 hours).

  • Would you like to share your glucose readings in real-time with a spouse or family member who is outside of the communication range of the system, or even in a different location? Remote viewing of glucose data allows parents to view your daughter’s glucose data while she’s in the middle of a hockey game, or your son’s data while he’s over a friend’s house. It allows you to view your own glucose data at a glance on a smart watch (without having to pull a receiver out of your pocket). All three manufacturers offer this option in some form or another.

  • Minimizing pain and discomfort is often a priority for parents when we are making decisions for our T1D children. If you want to use sensors that have the least discomfort on insertion, then you may want to chat with people who have used the different sensors to get their impressions, or check online forums and blogs for comments about insertion pain. Check with your diabetes health care team about trying out a sensor before you make a final decision – then you can see for yourself how comfortable the sensor is, on insertion and when wearing it.

  • The upfront costs and the cost of consumable supplies (sensors, transmitters, receivers) vary between manufacturers, as do how often you need to replace these different components, so you may want to check if the start-up and ongoing costs fit your budget. Also, some extended health insurance plans cover CGM and some do not; some cover Libre under “glucose meters” and some do not – check with your private insurer for details.

For a side-by-side comparison of the systems available in Canada:

The Bottom Line on Sensor Glucose Monitoring…

Continuous and Flash Glucose Monitoring systems provide a number of features that can help improve the efficiency and effectiveness of your diabetes care routine. By considering the similarities and differences between the different systems that are available in Canada, you can find a technology that meets your individual needs and preferences. I sincerely hope that the information on this page, in the summary CGM/Flash Comparison chart, and in the in the Managing Blood Glucose section of Waltzing the Dragon, helps you succeed in taming the diabetes dragon!

Tips from the Trenches

Despite all the ups and downs, we have found that glucose monitoring technologies are worth it! Our 14-year old son has worn both CGM and Libre on and off for the past 10 years. When he’s wearing a system, we can see clearly the effect that different foods have on his blood sugar, we get insight into the times that insulin doses need to be changed, and we can tell what happens overnight without having to get up and check. Overnight checks as a whole are easier, as we can glance at his glucose readings without getting out of bed, or even skip a middle-of-the-night check because we have Low Alerts as a back-up. Perhaps most importantly, when our son did not reliably recognize his lows, CGM gave us peace of mind.

On the flip side, he has had some significant issues with skin reactions, and we sometimes get false Low Alerts when he sleeps on the sensor (check out PISA), but as I said, the benefits have outweighed the drawbacks for our family.

More on what each system has to offer: