What Is A Continuous Glucose Monitor (CGM)?

What Is A Continuous Glucose Monitor (CGM)?

You may have heard about continuous glucose monitors (CGM) and wondered whether this technology might be right for you. 

This article will explain what this self-monitoring tool is, how it works, and whether it might help you manage your diabetes.

What is a CGM?

CGM stands for continuous glucose monitor or continuous glucose monitoring [1].

When you are diagnosed with diabetes, one of the first things that your team will tell you about is monitoring your blood glucose levels. Self-monitoring is one of the cornerstones of good diabetes care [1, 2, 3]. 

Self-monitoring, via finger-prick testing, allows you to measure your blood glucose at any given time and, importantly, helps you learn what causes it to go up or down [1, 2].

Self-monitoring is not without its challenges. Some cannot perform finger-prick testing by themselves, others may find the multiple finger-prick testing to be uncomfortable or painful [1, 2, 3]. The intermittent nature of finger-prick testing means that there can be significant periods (for instance, while you are asleep) when you cannot monitor your blood glucose [1, 2].

Continuous glucose monitoring (CGM) seeks to work around many of these problems, providing a convenient and comprehensive assessment of your blood glucose levels, which may allow you to manage your diabetes better [1, 3].

CGM systems measure glucose levels in the interstitial fluid (the fluid which surrounds our cells)), providing continuous information about your glucose levels [2, 3]. This can help to identify and prevent unwanted periods of hypo and hyperglycaemia [4].

How does CGM work?

A CGM consists of 2 or 3 parts depending on the device. The first is a hair-like sensor that sits just below the skin, usually on the upper arm or abdomen [1, 2, 3]. This sensor measures the glucose in the fluid surrounding it (known as the interstitial fluids) [1]. 

This measurement is sent to the second part of the CGM, the transmitter [5]. The transmitter then sends and/or stores this signal wirelessly (or otherwise) to the receiver/display device (usually an app on your smartphone) [5].

The display device (either a receiver or app on your smartphone) for most modern CGMs can display your current blood glucose, store previous readings, and help you to understand how everyday activities such as eating or exercise might affect your blood glucose levels, as well as how to manage these effects [1, 2].

The CGM sensor portion is disposable and must be changed every 5-14 days [2, 3]. Depending on the system, the transmitter and display components are reused with your next sensor to allow you to maintain continuous monitoring.

Who can use a CGM?

Most people using CGMs have type 1 diabetes, although evidence suggests that there may be a benefit for people with type 2 diabetes to use continuous glucose monitoring [1].

Continuous glucose monitoring may be ideal for people living with diabetes, especially people who experience hypoglycaemia unawareness. [1, 3]

If you aren’t sure whether you can — or should — use a CGM system, talk to your diabetes care team for further guidance.

Can I use a CGM and an insulin pump together?

An insulin pump (a continuous subcutaneous insulin infusion or CSII) is a device that some people use to provide their body with the insulin it needs to manage their blood glucose [5]. 

An insulin pump usually provides a continuous low dose of insulin (sometimes called a basal dose), which can be temporarily increased (a bolus dose) in response to eating, exercising, or readings from a glucose monitor [5].

Blood glucose measurement is usually undertaken by taking repeated finger-prick blood tests, measured using a traditional glucose meter [1].

This system can be changed by introducing a CGM, allowing the person to give insulin doses based on a continuous glucose reading rather than intermittent finger-pricks [5].  

What is an ‘artificial pancreas’ (Advanced Hybrid-closed loop insulin pump)?

To understand an artificial pancreas, it may be helpful to briefly think about what your actual pancreas does and how it is affected in type 1 diabetes.

When you eat, your food is digested, and carbohydrates are broken down into simpler sugars, such as glucose, which are absorbed into your blood [2]. Your pancreas detects these elevated blood glucose levels and secretes a hormone called insulin to bring your blood glucose levels back to normal levels [2]. In type 1 diabetes, damage to your pancreas stops it from secreting insulin to manage your blood glucose [5].

An ‘artificial pancreas’ seeks to emulate the function of a real pancreas by measuring blood glucose (through a CGM device) and then adjusting the rate of insulin being given as a continuous infusion into the body [5].

An artificial pancreas consists of a continuous glucose monitor connected to an insulin pump [1]. The pump uses information from the CGM and a algorithm to adjust the rate of the insulin infusion [1, 5].

Studies have shown that pumps that run in this manner can improve glucose control compared to conventional pumps [1].

Modern systems can also react to glucose excursions such as hypoglycaemia by reducing or temporarily stopping insulin infusion [5].

How can I get a CGM?

A CGM is a useful device that may help some people better manage their diabetes. At the present time, they are not available to everyone, but when used can be of great benefit [8].