What is CGM?

Continuous Glucose Monitoring (CGM) is always a hot topic of conversation in diabetes. With people talking about what it is, who can access it, how it can benefit you and more. But do you really know what CGM is and how it works? In this article we explain a few of the basics about CGM.

Continuous glucose monitoring (CGM) is a way of measuring your glucose levels continuously throughout the day and night. A sensor is inserted just under the skin and measures your glucose levels every few minutes, to provide a graph of your glucose levels over time.1

Use of CGM, alongside injection or pump therapy, has been shown to:

• Reduce HbA1c2-4, with the reduction higher in people with an HbA1c above target5
• Reduce the number of severe hypoglycaemic events experienced2,6
• Increase time spent in target range3
• Reduce time spent in hypo- or hyperglycaemia3,4

How does CGM work?

A small sensor sits just under the skin and is connected to a transmitter. This sensor measures your sugar levels over time, transmitting the information every few minutes to either a receiver or your mobile phone.1

Instead of single, spot measurements, like you get with standard blood glucose monitoring, you end up with a graph of how your glucose levels change over time.1 This real-time picture allows you to track whether your glucose levels are within, above or below target, as well as whether they are stable, rising or falling.7 This makes it easier to see how your diet, exercise and other health factors affect your glucose levels1, and also see how your glucose levels change at times when you would not normally be monitoring, such as while sleeping.7 The system can be set to alarm at high and low levels, to warn you when your glucose levels are outside of your target range.

Is CGM the same as blood glucose monitoring?

CGM is different to blood glucose monitoring as it does not measure your blood glucose level. Instead, CGM measures the glucose levels in your interstitial fluid (this is the fluid between the cells of your body).1 Glucose levels in your interstitial fluid can lag behind your blood glucose levels by up to 15 minutes, with this delay being longest if your blood glucose level is changing rapidly, e.g. after eating or during exercise.1 In order to ensure your CGM is as accurate as possible, it will need to be calibrated with a blood glucose check twice per day.1

CGM cannot be used as a replacement for blood glucose testing. Most of the CGM systems available in the UK are labelled as ‘adjunctive’. This means that the CGM reading alone cannot be used to make treatment decisions, you still need to check your blood glucose.8