Continuous Glucose Monitoring (CGM)
- How does the rtCGM system work?
- What is interstitial glucose?
- What is the difference between rtCGM and flash glucose monitoring?
- Advantages of using rtCGM
- Disadvantages of using rtCGM
- How do I get rtCGM?
- Can I buy a rtCGM system for myself?
- Useful resources
Real time continuous glucose monitoring (rtCGM) is a way you can automatically measure your glucose levels every few minutes throughout the day and night. It involves using a system that comprises a sensor, a transmitter and a handheld monitor on which you can read the results.
The rtCGM allows you to monitor your glucose levels and assess how they change while you are sleeping, after you eat, during exercise or when you are ill.
How does the real time CGM system work?
- The sensor is actually a small electrode that is inserted under the skin using an applicator device. The sensation is similar to having an insulin injection.
- The sensor measures your interstitial glucose levels.
- The sensor is connected to a transmitter which sends the data wirelessly to your handheld monitor.
These are some of the features of rtCGM:
- A visual display of your current interstitial glucose level
- A trend arrow indicating whether your glucose level is falling or rising
- A trend graph showing results over the last three, six or 24 hours
- An alarm setting to alert you when your glucose level is high or low
- An option to download data so that you can review it with your diabetes care team
What is interstitial glucose?
- Interstitial fluid is a thin layer of fluid around your tissue cells. Glucose levels in the interstitial fluid lag behind glucose levels in your blood by up to 15 minutes.
- The lag time is longest if your blood glucose level is changing rapidly, after eating or if you are exercising.
- Due to the lag time, you should also do a fingerprick blood glucose check if you are considering additional insulin or treatment for hypoglycaemia.
To learn more about blood glucose and interstitial glucose, watch the video below:
What is the difference between real time CGM and flash glucose monitoring?
rtCGM monitors your glucose level continuously and sends data to your display device on an ongoing basis. You can set it to alert you when your reading is high or low and you can easily view trends and patterns. With flash glucose monitoring, it is only when you scan your sensor that you can take a reading and see trends, although the Libre 2 flash glucose monitor alarms will sound even if you are not scanning.
Advantages of using rtCGM
- You can track your glucose levels throughout the day and night.
- You can see what your levels are like at times when you don’t normally test, e.g. during the night.
- You can see trends: when your glucose levels are starting to rise or fall, so you can take action earlier and avoid a hypoglycaemic episode (a ‘hypo’).
- Fewer fingerprick checks are necessary.
- It helps you achieve and maintain your target HbA1c level.
- You can set it to alert you when your glucose level is high or low.
Disadvantages of using rtCGM
- It is easy to become overwhelmed with the amount of data.
- You may find wearing the sensor uncomfortable or feel that it is unattractive.
- You need to be motivated to benefit from the data provided.
How do I get rtCGM?
It depends on whether you want to use the rtCGM for a short period (7–14 days) or long term. If you want to wear one for a week or two to help you look at your glucose trends, your clinic might be able to lend you one for that length of time. Then you can look at the data with your diabetes care team and decide whether you need to make any changes to the way you manage your diabetes.
If you want to use rtCGM long term, you will need to ask your specialist team or GP. Some rtCGM systems are now available on the NHS. There are strict criteria set by NICE (the National Institute for Health and Care Excellence) around who is eligible, and you need to meet these criteria in order to qualify for a prescription.
Click on the following link to see NICE guidelines on CGM and to learn more about funding options:
Can I buy a rtCGM system for myself?
Yes, but prices can vary, depending on which rtCGM you choose, and they tend to be very expensive. If you do go ahead and purchase your own, remember that you are likely to benefit most from the system if you get support in using it, so ask what support the company and your diabetes care team can give you.
Air travel and rtCGM
- It should not be exposed to full-body scanners (i.e. x-ray or millimetre radio-wave).
- To avoid removing your rtCGM you should request another type of screening to be performed by the security officer.
- If in doubt about the type of security scan you are passing through, notify the security officer prior to proceeding through the airport security checkpoint.
- Remember to bring medical evidence such as a letter from a medical practitioner, to confirm your medical device. Have this ready to show the security officer.
Medical device awareness card
Following a number of complaints regarding security officers asking people with devices such as rtCGM's or insulin pumps to either remove their device or go through body scanners, you can now carry a Medical Device Awareness Card.
The card contains information for both the passenger and security officer. It has been in use in the UK since 2019 and is endorsed by the ICAO Aviation Security Panel to improve global guidance on security screening for passengers with medical devices.
The video below gives more guidance on the Medical Device Awareness Card:
For information about the main manufacturers of rtCGM systems and their products, click on the following links: