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Continuous glucose monitoring (CGM)

For people with diabetes, it is important to know your precise blood glucose level (glycaemia) at all times.

This information allows people with diabetes to adjust their insulin therapy as required and to assess whether their blood glucose targets have been achieved.

Continuous Glucose Monitoring (CGM)

Proposed as an alternative to the standard finger-prick testing, continuous glucose monitoring (CGM) systems have been on the market since 2000. What exactly are these devices and how do they work? We take a closer look at a therapeutic tool that is making life considerably easier for people living with diabetes.

What is continuous glucose monitoring?

Continuous glucose monitoring has revolutionised the way that people with diabetes measure their blood glucose levels.

CGM systems display an individual's blood glucose levels, which they measure continuously and almost in real-time. They are specialised electronic devices comprising:

  •  a sensor placed under the skin that measures the concentration of interstitial glucose, usually at intervals of 1 to 5 minutes;
  • a transmitter which stores and/or sends the sensor readings to the receiver every 5 to 15 minutes;
  • a dedicated receiver that displays the data, for example, an insulin pump and/or a mobile device (a smartphone or smartwatch).

Some CGM systems allow the user to see their blood glucose measurement only on demand, by displaying the glycaemia log history.

The evolution of CGM systems

Since their initial launch, CGM systems have considerably evolved. Their size, weight, complexity, and cost have decreased while their features, user-friendliness, and interactive abilities have greatly improved. Data analysis has also progressed through specialised applications for managing and sharing data with family and clinical teams via the internet and smartphone applications.

Particularly useful for those who experience frequent, severe, and/or nocturnal hypoglycaemic events, pregnant women, children, and those with poorly-controlled diabetes, continuous glucose monitoring is valuable in improving diabetes management.

How do CGM systems work?

The latest versions of CGM systems use a fine needle inserted just under the skin of the abdomen. A tiny sensor on its tip measures the level of glucose in the interstitial fluid.

What is the lifespan of a sensor?

Sensor lifespans vary between 7 and 14 days depending on the manufacturer. There are also sensors that can be used for 90 to 180 days. 

Some models of CGM need calibrations by measuring the blood glucose every 12 hours, while others have eliminated this particular requirement.

The sensor measures the level of glucose in the interstitial fluid surrounding the subcutaneous skin cells, and not the actual level of glucose in the blood. This means that the changes are observed slightly later than the real changes in the blood glucose level. This delay is explained by the fact that it takes time for the glucose to move from the blood to the interstitial fluid.

In stable blood glucose periods, the average lag is around 5 minutes. However, during episodes with rapid changes in glycaemia, for example, after a carbohydrate-heavy meal or physical exercise, the lag can be greater than ten minutes.

Today, measurement error margins of CGM systems have been halved, from 20% to 10%. This level of reliability is precise enough to allow self-adjustment of insulin doses.

CGM and insulin pump

A CGM system is also often connected to an insulin pump which automatically adjusts insulin delivery based on the glycaemia measurements. This allows corrective insulin bolus volumes to be determined with precision, and if hypoglycaemia is detected, insulin infusion from the pump is temporarily suspended.

Multiple studies comparing usage of CGMs and glucose meters have shown that continuous glucose monitoring:

  • provides better blood glucose management
  • increases time spent in optimal blood glucose range
  • reduces the risk of hypoglycaemia and hyperglycaemia

CGM systems have greatly improved the quality of life for people living with diabetes by reducing stress and optimising decision making.

Find out more about Dexcom CGM integration

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Sources

  1. M. Langendam et al. Continuous glucose monitoring systems for type 1 diabetes mellitus (Review), Cochrane Database of Systematic Reviews 2012, Issue 1. Art. No.: CD008101.
  2. Klemen Dovc, Tadej Battelino. Evolution of Diabetes Technology. Endocrinol Metab Clin North Am. 2020 Mar;49(1):1-18. doi: 10.1016/j.ecl.2019.10.009. Epub 2019 Dec 4.
  3. D. Rodbard. Continuous Glucose Monitoring: A Review of Recent Studies Demonstrating Improved Glycemic Outcomes Diabetes technology and therapeutics. Vol. 19, supplem. 3, 2017.
  4. D. Rodbard. Continuous Glucose Monitoring: A Review of Successes, Challenges, and Opportunities. Diabetes technology and therapeutics, Volume 18, Supplement 2, 2016.

About Making Diabetes Easier

Air Liquide Healthcare UK is committed to improving quality of life for people with diabetes. Our healthcare teams provide patients and their loved ones with education, support and personalisation of care.

Our mission? #makingdiabeteseasier

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