Greater Glasgow and Clyde Child & Adolescent Diabetes Service 

FAQ - Continuous Glucose Monitoring Systems

A topic of great interest to many people with diabetes is the use of Continuous Glucose Monitoring Systems (CGMS).  Here we try to answer some Frequently Asked Questions on the subject.  As always, the team are happy to discuss CGMS with you if you want to know more.

What is CGMS?

Continuous Glucose Monitors do exactly what they say they do - they measure glucose in the body and transmit that to a device (e.g. an insulin pump or a mobile phone) so that an individual can respond to that data in real-time.

If it's not measuring blood glucose, what is the point of CGMS?

It is possible to use CGM on its own, i.e. in conjunction with injection regimens, but most use by patients is linked with an insulin pump. There are two systems in use which work with different pumps but more are in development. These are described here (in alphabetical order):

How is CGMS used by patients?

It is possible to use CGMS on its own, i.e. in conjunction with injection regimens, but most use by patients is linked with an insulin pump.  There are two systems in use which work with different pumps but more are in development.  These are described here (in alphabetical order):

Dexcom G6 and Dexcom G7

Dexcom sensors can send data either to a handset or a compatible mobile phone, or a compatible insulin pump.  This device can then set of an alarm when it detects the glucose reaches either high or low limits, or when it predicts the user may be about to become hypo.  If a mobile phone is used, other phones can be linked to receive data, meaning that parents can be alerted to potential problems even when their child is in another room.

Dexcom markets their sensors as requiring no finger-prick glucose tests, which has attracted many people to it.  There are times, however, when blood testing is necessary.

FreeStyle Libre 2

Many are familiar with the Libre 2, as it is available to most people with diabetes.  Our page here gives more information on the Libre 2.

At present, the Libre 2 does not communicate with the insulin pumps we provide but it is expected that this will become available over coming months.

CGMS sounds brilliant so why isn't everyone using it?

Like insulin pumps, CGM may not benefit everyone.  However it's fair to say that one of the biggest reasons is cost.  NHS funding for CGM is limited and we as a diabetes team have had to prioritise those patients we feel are at most clinical need.  This may seem unfair to families who work very hard to control the diabetes, but funded CGM is simply not available for everyone at the moment.  We hope this situation will change in the future.  We will, however, provide CGM for anyone using a compatible insulin pump - see our page here for more information on pumps.

How much does CGMS cost?

This is not a straightforward question because it depends upon factors such as device and continuous versus intermittent use.  Both Dexcom and Medtronic have different price structures for NHS versus individual buyers, and deals for agreeing to use CGMS for longer periods.  However, a ballpark figure for continuous use for a year is £2000-3000.

The system most commonly used in the UK involves a inserting a small sensor under the skin (placed exactly like a cannula for an insulin pump) and this uses a chemical reaction to measure the glucose level.  However it is very important to note that what is being measured is NOT the blood glucose but that of the interstitial fluid (the "tissues" that surround the blood vessels) because they are not the same.  The tissue glucose generally lags about 10-15 minutes behind the blood glucose but can be further affected by factors such as temperature, so a blood glucose test may give a different reading to tissue glucose measured at the same time.

Can I share CGMS data with the diabetes team?

Yes, and for us to look after patients as well as we can it is important that we have access to these data.

Click here for more information.

If I am admitted to hospital, can I keep using my CGM?

As long as you are well enough and do not need an X-Ray or other scan, you may keep your glucose sensor in place.  However you should know that results from it will not be used to make clinical decisions during your stay. Because of the possible differences between tissue glucose and blood glucose, especially during times of illness and stress, nursing staff will continue to use finger-prick blood glucose tests to decide on things like insulin doses.

Medtronic Guardian

Typically used with a Medtronic insulin pump, the Guardian system does much the same as the Dexcom.  When used with older pumps, the Guardian can predict when a hypo is likely to occur and suspend the insulin delivery.  With more recent Medtronic pump, it can also adjust the background insulin to give more insulin when it sees the glucose is rising.

The Guardian 4, used with the Medtronic 780G pump, also does not require routine fingerpricks but some may be required on occasion.  Phone apps are also available to view and share data.

Some families decide to pay for CGM themselves. If you are thinking about doing this, please discuss it with the team in advance.