A new generation of continuous glucose monitoring (CGM) devices takes the pain out of blood glucose testing. 

Ever since their invention in the 1970s, blood glucose meters have undergone major transformations. The current crop of continuous glucose monitoring (CGM) devices has emerged as a new standard of care for many people with insulin-treated diabetes, allowing them to assess glucose levels and trends 24 hours a day through a continuous stream of data – all without the multiple daily fingerstick testing of traditional self-monitoring.  

Currently, two types of CGM are available for daily diabetes self-management; real time CGM (rtCGM) and intermittently scanned continuous glucose monitoring (isCGM) which is often referred to as “flash monitoring.”  

Both types provide people with diabetes, their healthcare providers and caregivers with actionable information about current glucose levels and trends. The CGM data can be analyzed to gain a more complete picture of the glycemic patterns throughout the day or night. CGMs also provide insight into the duration, frequency and causes of blood glucose fluctuations. By identifying impending periods of hypoglycemia and hyperglycemia, users can make adjustments to food, activity and medication to stay in their target range.   

There are many brands of CGM devices today, ranging from basic models to more advanced ones with multiple features and options. But along with choice comes challenges. How tech-savvy do people have to be to use them? How do they store data? Can users share their readings with others in real time? And last but not least, will insurance cover the cost?  

Understanding the differences between the two CGM systems can help healthcare providers guide patient selection to the system which best meets their individual needs. Let’s take a closer look at the two main types. 

Readings taken from interstitial fluid, not blood 

Both rtCGM and isCGM devices measure glucose concentrations in the interstitial fluid, a thin layer of fluid under the skin which surrounds the body’s cells. They include a small disposable sensor that is worn under the skin (often on the stomach or arm) which checks glucose in the subcutaneous tissues, and then displays current glucose values and trend information (e.g. graph, arrows) on an external device. However, there are key differences in how they provide the readings. 

Current rtCGM systems transmit glucose data (trend and numerical) in real time to a receiving device such as a watch or smartphone. They also provide programmable alarms and alerts to warn users of impending hypoglycemia or hyperglycemia. These real-time alerts can be shared with caregivers. This device requires twice-daily calibration with fingerstick blood glucose testing. 

The isCGM system continuously samples and measures interstitial glucose levels, generating a new value every minute. But unlike rtCGM devices which automatically transmit a continuous stream of data to the user’s receiver and/or smart device, CGM users have to scan the sensor at least every eight hours. If not, the glucose information will not be available for decision-making or later download.  In addition, the system does not offer alerts or alarms. 

How does this translate into meaningful outcomes? 

Numerous clinical trials have demonstrated the safety and efficacy of these systems as stand-alone devices. According to Diabetes Canada, CGM systems can be used to help people with diabetes stay within their blood glucose range and prevent hyperglycemia and diabetic ketoacidosis. If used consistently, they have the potential to prevent life-threatening emergencies. 

Combining CGM and Insulin Pump Technology

Another major advancement in diabetes treatment has been connecting the technology of CGM and insulin pumps into one closed system. Called “closed loop” or artificial pancreas option, it combines a CGM, an insulin pump and an algorithm to automatically and safely deliver basal (background) and rapid (meal-time) insulin to provide optimal glycemic control.

Who could benefit from CGM? 

Both devices are well suited for people with diabetes who want to get frequent feedback to see trends and patterns in their blood glucose and adjust their therapy accordingly. Individuals with an increased risk of hypoglycemia, particularly those who have nocturnal hypoglycemia, should consider using rtCGM.  Good candidates for isCGM are those who are motivated to scan their device several times a day and do not need alerts or alarms. 

Cost of course, needs to be considered.  Not only are CGM devices expensive depending on the brand, but parts need to be replaced in some cases. While some private plans provide CGM coverage, public coverage is inconsistent across Canada. That said, Diabetes Canada recommends that provincial governments publicly fund CGM for people with diabetes when there are demonstrated improved health outcomes. 

As with all new technologies, safe and effective use of isCGM, rtCGM and closed loop systems requires thorough education and training. Learn more about CGM systems in our complimentary expert video brief: 

Advances in Blood Glucose Monitoring and Insulin Delivery 

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