Continuous glucose monitoring (CGM) systems
Technology towards a ‘closed-loop’ artificial pancreas had moved one step further as wireless continuous glucose monitoring (CGM) systems have been established in the UK. With this ‘closed loop’ system, a person would wear an insulin pump that was connected to a continuous glucose monitor. The pump would then deliver the correct dose of insulin automatically as it received information from the CGM monitor in ‘real time’.
Continuous Glucose Monitoring (CGM) is currently used to monitor blood glucose so people can achieve the best blood glucose control. It is particularly useful for people who have consistent glucose control problems on insulin therapy because CGM:
• Gives greater insight into glucose levels throughout the day
• Determines the benefits (or otherwise) of medication changes
• May help identify and prevent unwanted periods of hypo and hyperglycaemia
The ‘real time’ CGM system available in the UK measures blood glucose levels every five minutes 24 hours a day and displays the results on a monitor. In Ireland the system used is not wireless and instead of displaying information on a monitor, after three days the person wearing the device attends the hospital where the results are downloaded. This then gives the results on the previous three days’ tests.
It is very important to remember that if you use an insulin pump it is not linked to the CGM.
Where is CGM useful?
Both traditional and ‘real-time’ CGMs are often used for different purposes. The traditional CGM is mostly used as a diagnostic tool for a short time whereas the ‘real-time’ monitors are mostly used in those who are willing to undergo intensive insulin management and/or hypoglycaemia control.
The traditional CGMs are particularly useful in adults and children to identify overnight glucose profiles and postprandial (after eating) hyperglycaemia. This means your therapy can be adjusted to get the best results.’Real-time’ CGMs can also be used like this but in addition they can be used for longer periods of time (2-3 months) in those that want intensive therapy and education.
People with diabetes can improve their management of diabetes with the ‘real-time’ CGMs because they show how your blood-glucose levels react to:
• Physical activity
• Different medication types and doses
Studies have shown that the use of ‘real-time’ monitors may improve the time people stay within their blood glucose target range because they can:
• Reveal hyperglycaemia
• Show reductions in hyperglycaemia without associated increased hypoglycaemia Improve HbA1c
CGM can also:
• Help pregnant women to achieve better glycaemic control and to reduce time with hypo and hyperglycaemia-this is important because good glycaemic control reduces the risk for mother and baby.
• Helps athletes to diagnose nocturnal late-onset hypoglycaemia
• Help people to manage their diabetes better.
How does CGM work?
A CGM is a tiny glucose sensor that sits under the skin. It measures the amount of glucose in your interstitial fluid not in the blood. This means that this measurement and the measurement of blood glucose can often be different, particularly when there is a rapid change of glucose.
In ‘real-time’ CGMs, the interstitial reading is then displayed on the meter. In other monitors the reading will be downloaded onto the computer when the person returns to their diabetes team.
In all CGM systems the information is downloadable onto a computer and can plot the trends in the person’s capillary blood glucose levels over 24 hours. These can then be matched with a person’s capillary blood glucose tests and also with their diary. This can help to provide information on:
• Hypo unawareness
• Nighttime hypoglycaemia
• Insulin intake
• Activity levels
• Dietary intake
• Stress levels
It is important to note that the ‘real-time’ CGM measures interstitial fluid not capillary glucose. Increasing glucose changes are seen first in the capillary glucose and therefore the sensor has a lag time of up to 10 minutes depending on how quickly the glucose level is changing.
The ‘real-time’ CGMs have an alarm that can set by the person with diabetes and their healthcare professional to alert them if their blood glucose levels go outside of their individually set target range. However, the person will still need to calibrate their blood glucose levels with a capillary blood glucose test due to the delay in the monitor displaying the information and the accuracy of the interstitial fluid reading.The alarm systems may reduce the duration of hypo and hyper glycaemic excursions by alarming at set glucose targets.
When should CGM by used?
Adults and children who have persistent problems with hypglycaemia unawareness or repeated hypoglycaemia should be offered CGM to help determine where and why this is happening.
When ‘real-time’ CGMs are introduced in Ireland, you should be aware that they take time to learn to use. A one-off three-day period may not be enough to learn how to use the system and to gather enough data and learn from the results. People using ‘real-time’ CGMs need to be well motivated and have a good basic understanding of their diabetes.
‘Real-time’ CGMs need to be used in conjunction with good education and support. Any medical decisions should also take into account your A1c and capillary glucose levles – and not rely just on CGM information alone.
For the future
In the long term, it is hoped that the ultimate diabetes managment system will be developed into a closed loop artificial pancreas that will monitor blood glucose levels and dispense insulin accordingly. However, in the mean time CGMs provide information to the person with diabetes and their healthcare professional that can aid in improvement of A1c levels and blood glucose control.
Anne Clarke, Health Promotion and Research Manager, Diabetes Federation of Ireland
Sheila O’Kelly Diabetes Ireland Volume 7 Issue 1 Spring 09