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Posted: February 13, 2024

Continuous Blood Glucose Monitoring

In this image, a man holds a mobile phone and checks his blood glucose.

Advances in blood glucose monitoring

Managing Diabetes Highlights:

  • Continuous blood glucose monitors are an alternative to painful finger pricks
  • New technology is able to monitor and automatically adjust insulin doses
  • Discover how new monitors and insulin pumps are changing the game for diabetes care

The first versions of these devices were introduced in 2014 and have been widely available in Canada since 2018. The technology uses a sensor and a reader to monitor glucose levels in the interstitial fluid.The sensor is attached to the body. A reader or a free app installed on a cell phone is used to check glucose levels. A Real-Time Continuous Glucose Monitor (rtCGM) uses Bluetooth technology to provide constant communication between the cell phone or the reader. An Intermittently-Scanned Continuous Glucose Monitor (isCGM) requires the user to swipe the reader or cell phone across the sensor. All of the devices can potentially provide glucose results 24 hours a day, seven days a week, and will store data for the past 90 days.

Not only do these devices make it easier to collect results, they also provide more valuable information. The user can tell where their glucose has been, as well as where it is going. The rtCGM and isCGM trend arrows show if glucose is going up or down quickly and needs attention, or if it is level and not a concern.

The rtCGMs and isCGMs work in pretty much the same way. A sensor, roughly the size of a toonie, is placed on the skin, usually on the arm or abdomen. A small plastic tube, about the diameter of a fishing line, is inserted from the sensor under the skin. Applying the sensor is not painful, and is easy to do. Each sensor lasts between 7 to 14 days, depending on the device.

A rtCGM usually has three parts to the system: a sensor, a transmitter, and a reader. While the sensor on a rtCGM lasts 7 to 10 days, the transmitter lasts three months. Each time a sensor is changed, the transmitter must be removed from the used sensor and applied to the new sensor.

Generally, the user is able to easily apply the sensor for both devices. Manufacturers include detailed, easily-followed instructions in the packaging and on their websites. Links to videos showing how to apply the sensors can be found on manufacturer websites as well as on YouTube.

The rtCGMs and isCGMs do not measure glucose in exactly the same way that a blood glucose monitor does, and so may not show the same results. A blood glucose monitor measures glucose in the blood. The rtCGM and isCGM sensors measure the glucose found in the fluid around the cells in the body. This fluid is called interstitial fluid. Glucose in the blood passes through the blood vessel walls into the interstitial fluid. The time it takes for this transfer process can cause a slight delay in the readings. However, just like cars on a subway, all are going to the same place within a few seconds or minutes of each other.

In this image, a man holds a mobile phone and monitor blood glucose.

Think of the differences in results between capillary blood glucose monitoring and CGMs as the front and back of a train. The first car (the capillary blood glucose monitor) arrives before the last car (the CGM). The capillary blood glucose results show immediate glucose, while the CGM readings have a slight delay. Both results are correct, even though at any given moment they may not be identical.

In the past, rtCGMs had to be calibrated twice each day using a blood glucose monitor with finger pokes. However, most current CGM devices do not need calibration. If glucose readings are very high or low, users will sometimes be prompted to check their glucose levels using a blood glucose monitor to confirm results. However, under most conditions rtCGMs and isCGMs are considered accurate, and the readings are reliable.

The Freestyle Libre and Freestyle Libre 2 are isCGMs, which require a reader or phone app to swipe across the sensor at least every eight hours to capture all of the data. A rtCGM such as Dexcom G7 or Medtronic Guardian uses Bluetooth technology to send glucose results continuously to a compatible reader or cell phone app. These devices are programmed to signal an alarm when glucose levels rise or fall too quickly, warning of possible highs or lows. While rtCGM alarms cannot be disabled, they can be adjusted to the user’s preferred settings. Users can also adjust or disable the alarm settings that are available on the Freestyle Libre 2.

Some rtCGM devices can be linked to an insulin pump. With this link, the pump can automatically adjust insulin delivery based on a program set by the user and on current glucose readings. These rtCGMs are made by the pump manufacturers to work with their specific insulin pumps.

All rtCGMs and isCGMs can download information to a computer. A device-specific app also allows data to be sent in real time via the Internet to doctors or other members of the diabetes care team. This function helps parents or guardians of fragile adults to monitor glucose levels remotely. Device manufacturers provide simple instructions on how to allow this sharing of information.

When choosing glucose monitoring technology, consider your personal situation. Do you have type 1 or type 2 diabetes? Are you pregnant? Are you using insulin or an insulin pump? What type of insurance coverage do you have? Work with your diabetes health care professional to consider your unique needs and the type of monitoring thought best for you.

New Terms

In a recent update to the Diabetes Canada guidelines, the expert committee has set out new terminology to describe the different types of glucose monitoring. These terms, summarized in the chart below, reflect the evolving innovation in monitoring technology.

Original TermUpdated TermNew AbbreviationDescription
Self Monitored Blood Glucose (SMBG)Capillary Blood GlucoseCBGMeasures blood glucose in capillaries by poking the finger.
Flash Glucose Monitoring (FGM)Intermittently-Scanned Continuous Glucose MonitorisCGMMeasures glucose in the interstitial fluid by scanning a sensing device with a reader or phone over a sensor. The data can be viewed on the device at any time on a real- time display.
Continuous Glucose Monitoring (CGM)Real-Time Continuous Glucose MonitorrtCGMMeasures glucose in the interstitial fluid using a sensing device that continuously sends the data to a reader or iPhone app. Data is available on the device at any time on a real- time display.

Many people make their choice based on funding from their insurance company or their provincial public drug benefit program. Costs for different kinds of monitoring technology can vary as can coverage for such items. If you are considering new monitoring technology, it is prudent to determine the costs ahead of time and to check with your insurance plan to learn more about the coverage available to you.

Gathering valuable information on blood glucose levels

The rtCGMs and isCGMs are usually used by people using insulin. Diabetes Canada now recommends considering an rtCGM device for anyone taking more than one shot of insulin per day. Anyone with diabetes can benefit from using these devices, even for a limited time. They will:

  • see the effects of food and physical activity on food glucose levels
  • know what happens to their glucose while they sleep
  • better understand how their treatment plan is controlling their glucose.
Smartphone showing different types of graphs for monitoring Diabetes and generating reports.

These new technologies are game changers. With just a quick swipe, people can know what their glucose level is and where it is headed.

Although a cure is not here, managing diabetes becomes easier and a lot less painful with a rtCGM or isCGM. If you would like to learn more about these options, please speak with your diabetes care team.

Accessing financial support

Financial assistance may be available from provincial public drug benefit programs and private insurance companies. Before funding is given, prior authorization is usually required. The first step may be a doctor making a special request to the provincial health plan to access funding.

Before making any purchases, it is important to check which items, makes and models are covered.

  • Not all provincial public drug benefit programs or private insurance companies include all makes and models of rtCGMs and isCGMs.
  • Some provincial public drug benefit plans only cover part of the cost of rtCGMs and isCGMs, but there may be specific requirements for coverage. For instance, users may have to be on an insulin pump or use two types of insulin for coverage.
  • Some plans cover the cost of sensors, but not the readers. However, some companies will provide a free reader once they are sent proof that a CGM has been purchased.
  • Some insurance company plans only cover rtCGMs. Others will only approve isCGMs, even if the user is on two types of insulin or an insulin pump. The rules are complicated for provincial government funding and differ widely throughout the country. It is very important to check out funding with provincial pharmacare government agencies prior to purchasing a CGM to see if you qualify for assistance with costs. You may need to apply for special authority from the government, and only one type of CGM device may be covered. The same is true when relying on private insurance companies for assistance. Always check with your insurance to ensure that the device you hope to purchase is included in your insurance coverage before you buy.

Some companies offer compassionate care programs to low-income people who are not covered under private insurance or provincial public drug benefit programs. A doctor’s office must send a compassionate care request to the company’s administrators. Usually, income must be verified.

For more information:

This 2022 Managing Diabetes article was written by Gerri Klein, RN, MSN, CDE, a national editor for the Canadian Journal of Diabetes selected as the 2020 Diabetes Canada Educator of the Year.