Bethany Kelly
Clinical Lead Diabetes Specialist Nurse
Amanda Williams
Lead Nurse for Diabetes and Endocrinology, East Kent Hospitals, Diabetes Forum UK
Continuous glucose monitors (CGMs) offer real-time data to aid diabetes management. In the UK, most insulin users are recommended CGMs, but only non-adjunctive types are approved for insulin dosing without finger pricks.
What is a CGM?
CGMs are small wearable devices that display real-time glucose levels. They help people with all types of diabetes better understand their patterns; make safer decisions on their treatments; avoid dangerous highs and lows; and make informed insulin decisions. As technology advances, CGM has become a key tool in personalising diabetes care.
What does safety look like?
In the UK, CGMs are now recommended for most people who use insulin, including those with type 1 diabetes and some with type 2, type 3c and gestational diabetes. However, not all CGMs are suitable for insulin dosing. Some are ‘adjunctive’ and require a capillary glucose measurement as a confirmation, while ‘non-adjunctive’ CGMs are approved for direct insulin decisions.
Our understanding of a CGM’s safety and accuracy depends on how and where it has been tested. A device may perform well, but without data from real-world conditions — such as during meals, insulin use or rapid glucose changes — its effectiveness in those situations remains unknown. International guidelines recommend that CGMs be evaluated under these challenging conditions to ensure their reliability in everyday use.
Accuracy is critical. Common figures, once used to assess accuracy, like MARD (mean absolute relative difference), can be misleading. MARD is an average value and may mask significant inaccuracies at the extremes of low or high glucose levels. The 20/20 and 40/40 accuracy metrics are more meaningful, showing how closely CGM readings match lab-tested blood glucose levels. Devices scoring highly on these metrics offer greater safety for people adjusting insulin based on CGM data.
In the UK, CGMs are now
recommended for most
people who use insulin.
Everyday practicality
Practical features help people find the right fit. Some sensors last seven days, others 14 or more. Some link with smartphones or insulin pumps, or allow family members to share data. Many offer alerts for glucose highs, lows or rapid changes. These can support daily routines, safety and peace of mind.
Diabetes specialist nurses are key to helping people choose a CGM that fits their clinical needs and lifestyle. They consider not just cost, but also safety, regulatory approval, device usability and compatibility with hybrid closed-loop systems.
Want to learn more?
For impartial comparisons of CGM systems, check out the DSN Forum UK’s up-to-date resources:
www.diabetesspecialistnurseforumuk.co.uk
Pleus, S., Eichenlaub, M., Eriksson Boija, E., Fokkert, M., Hinzmann, R., Jendle, J., Klonoff, D.C., Makris, K., Nichols, J.H. & Pemberton, J., 2024. The Need for Standardization of Continuous Glucose Monitoring Performance Evaluation: An Opinion by the International Federation of Clinical Chemistry and Laboratory Medicine Working Group on Continuous Glucose Monitoring. Journal of Diabetes Science and Technology, p.19322968241296096.
