Like many others with diabetes, you are probably already very aware of possible complications. Yet good blood glucose control may seem out of reach. Perhaps your fear of hypoglycemia is limiting you in achieving glucose targets. Although you monitor your blood glucose regularly, the results only show information about that point in time. You have no alerts when your glucose rises or falls, or ways to see trends in your glucose levels. Could continuous glucose monitoring technology help you?
CGM constantly reads data, every one to five minutes. This provides roughly 288 to 1440 readings daily, compared to four to eight fingersticks per day. It tells a story about your blood glucose, rather than taking a snapshot. With CGM, you see where your blood glucose level has been and the direction it is headed. Being able to predict a fall or rise in glucose acts as a guard against hypoglycemia or prolonged hyperglycemia.
The CGM system consists of three basic parts – a sensor, a transmitter, and a receiver.
The glucose sensor, a very fine, flexible filament, is inserted with an automatic insertion device. A needle, housed within the insertion device, places the glucose sensor under the skin. Then the needle is removed, leaving the glucose sensor sitting within fatty tissue and tissue fluid (also called interstitial fluid). The sensor reacts with molecules within the tissue fluid and sends a current up the filament to the transmitter. Although these sensor values relate to blood glucose, they are not exactly the same as self-monitored values. Instead, these sensor values relate tissue fluid amounts to blood glucose concentrations. It is also partly due to the lag time of these readings.
A transmitter is attached on top of the sensor. It rests on the skin and collects data. The blinded CGM Phil tries (see case study below) does not transmit signals to a receiver. Rather, all the data is collected, and can be downloaded to a software program once removed.
In contrast, a real-time transmitter sends signals to the receiver. This data is converted into a measurement of glucose (in mmol/L). Each transmitter has a unique ID and is linked to the receiver before a new sensor is inserted. The transmitter can be rechargeable or have a long-lasting battery, depending on the make and model.
The receiver is either a stand-alone, battery-powered unit, or is integrated into an insulin pump. A stand-alone receiver is about the size of a small cell phone. It can be carried in a pocket or worn in a case or on a belt. Mobile-connected CGM, new to Canada, uses Bluetooth technology built into the transmitter. Measurements can be viewed remotely on a compatible smart device.
The transmitter and receiver are reusable or rechargeable, lasting between six months and two years depending on the system. Sensors can be worn continuously for six to seven days. After being worn for three to seven days, the sensor is disposed of in a sharps container.
The CGM receiver displays glucose values every five minutes, and graphs trends from one to 24 hours. Important trends are displayed with arrows that indicate whether glucose values are rising or falling. Receivers can be programmed and customized to achieve specific goals for each user.
Phil has type 1 diabetes. He treats his diabetes with multi-dose insulin injections, and monitors his blood glucose levels using fingerstick testing. Phil usually tests his blood glucose when he wakes up. Before each meal, he tests again to determine how much insulin to take. Most of the time, he tests before going to bed.
Phil’s typical blood glucose values over the course of a day (simplified)
|Fasting||Before breakfast||Before lunch||Before dinner||Before bed|
|9.5 mmol/L||7.2 mmol/L rapid insulin||3.8 mmol/L rapid insulin||6.8 mmol/L rapid insulin||8.4 mmol/L basal insulin|
At an appointment, Phil’s diabetes care team suggests that he try using a continuous glucose monitor. The monitor would collect data 24/7, allowing the team to fine-tune his insulin regimen. Phil will continue to take his usual insulin doses and self-monitor with fingersticks. As well, he would note his day-to-day activities and food consumption.
Although Phil thinks he is managing his diabetes just fine, he decides to try CGM. His team explains that there are two different types of CGM. He will wear the first type, a blinded, retrospective sensor. The second type, called a real-time CGM, tracks glucose levels via a receiver. He can learn more about both during another appointment.
Phil has a sensor inserted, and returns to the diabetes care centre a week later. His team downloads the data. They compare it to his blood glucose monitoring record and his journal entries about activity and food consumption.
When Phil sees the graph format of his blood glucose values, it looks like a mass of spaghetti to him. It actually shows varying blood glucose readings (see table below). Phil is surprised by some of the information. In graph form, it is easy to see that between fingerstick measurements, he is experiencing hyperglycemia as well as hypoglycemia. He was not aware of these events, even though he was checking his blood glucose several times a day.
Since the CGM was blind, Phil could not see the data until it was downloaded. The results show that on half of the nights, Phil’s levels dipped below 4.0 mmol/L. He also had several hyperglycemia events after breakfast and supper. As the fingerstick tests only show one point in time, these events were never identified.
Seeing this information encourages Phil to learn more about this technology, and how to use real-time CGM.
Phil wakes up in target range, and avoids hyperglycemia after breakfast with a new insulin-to-carb ratio. An alarm that goes off before lunch helps him to avoid hypoglycemia. In the afternoon his blood glucose is steady, so he decides it’s a good time to be physically active. Before supper, Phil tests his blood glucose and checks the CGM. Since the arrow is trending down, he uses a reduced bolus with his meal.
Phil adapts to using CGM. He is using trends, along with directional arrows for glucose values, to help him make decisions about food and activity, as well as insulin dosing.
One type of CGM, integrated into an insulin pump, can suspend insulin delivery if a pre-set low glucose threshold is crossed. As this prevents blood glucose from going any lower, it improves safety for the user.
Another CGM was recently approved by Health Canada as ‘non-adjunctive’ therapy. The new CGM system can replace fingerstick glucose testing when making diabetes treatment decisions. If symptoms do not match the readings, fingerstick testing should continue. Regardless of system, the user must still use fingersticks at least every 12 hours to calibrate any continuous glucose monitor.
Research shows that daily use of real-time CGM can reduce A1C and hypoglycemia. However, other considerations must be taken into account with daily, continued use. A financial cost exists. Most provincial plans don't cover the cost. However, some coverage may be available through private or third party insurance. Skin health can be an issue, especially if the skin is sensitive to adhesive. Care must be taken with injection techniques and proper site rotation. Accurate calibrations are essential, using appropriate timing and fingersticks. Finally, users may feel ‘alarm burden’ or ‘alarm fatigue.’ This is especially likely if too many alarms are set, or alarms are not customized to the person’s targets and needs.
Although CGM provides a wealth of useful information, it can be overwhelming. In order to be a useful tool, the CGM must be customized to your needs and expectations. Your diabetes care team can provide advice and discuss the option of using CGM as part of your diabetes management.
For glucose management, Diabetes Canada recommends linking CGM and self-monitoring of blood glucose (SMBG) with an education and therapy program. The program should educate users about behaviour changes that will improve blood glucose levels. Diabetes Canada also recommends that for those with type 1 diabetes, real-time CGM may be used to improve blood glucose control and reduce hypoglycemia.
Only a small percentage of people use insulin pump therapy. CGM is not always added to insulin pump therapy, as there is a belief that people using it have better glucose control. However, two different insulin pumps are capable of linking to CGM. A range of studies with type 1 diabetes showed improved blood glucose control when insulin pump therapy was combined with CGM. A study compared long-term use of real time CGM, combined with either multiple daily dose insulin injections (MDI) or with insulin pump therapy, to standard SMBG. Using CGM added significant glucose control benefits. As well, A1C decrease was sustained, and there was less hypoglycemia.
One observational study found that using an insulin pump was not required to benefit from real-time CGM. Whether people used MDI or insulin pump therapy, blood glucose control improved through significant reductions in A1C. These improvements applied regardless of whether the diabetes was type 1 or type 2.
In another CGM study, blood glucose control again improved whether participants had type 1 or 2 diabetes, or used MDI or insulin pump therapy.
In the most recent research, the DiaMondD study, CGM was used with MDI. It found that no matter the person’s education, math ability or age, CGM was not too complicated to use. This study also confirmed that people would use CGM long-term (24 weeks). Results showed significant reduction of A1C, without the risk of hypoglycemia.