Continuous glucose monitoring (CGM, for short) is a system that allows people with diabetes to detect trends and patterns in their glucose levels. Instead of using blood – like a traditional blood glucose meter – a CGM system uses interstitial fluid (the clear fluid that surrounds the cells in your body) to determine a glucose value. Interstitial fluid mimics the same trends that blood glucose does.
So, what are the benefits of a continuous glucose monitoring system?
A CGM system senses and records your glucose levels every 5 minutes, which means it can show real-time trends – whether they are rising or falling. In contrast, blood glucose meters provide you with only a measurement (or “snapshot”) of your blood glucose levels at a particular point in time. So, with blood glucose meters, you can take corrective action only after you learn of a high or low reading. However, with a CGM system, you can see the trend in your glucose level as they develop.
CGM systems provide users with the ease of checking glucose levels throughout the day and preventing highs and lows, without the multiple fingerstick testing that’s associated with traditional blood glucose meters. They also offer users tighter control over blood glucose levels; that’s because most CGM systems have a built-in alarm that sounds if you’re getting close to a pre-set high or low.
Bear in mind, though that CGM is not a replacement for blood glucose monitoring. All diabetes-related treatment decisions must be made based on a fingerstick reading. In addition, your CGM will require a minimum of one fingerstick reading to be entered for calibration every 12 hours.
Perhaps most importantly, CGM systems can help identify long-term trends in your glucose levels– trends which often remain undetected in people who used traditional blood glucose meters – such as changes in levels while you’re sleeping, between meals, and during and after physical activities. The immediate feedback and longer-term trends provided by CGM systems are the key to understanding your individual response to exercise and food intake.
It’s common for people with diabetes to experience low blood glucose levels during and after exercise. That’s because, as your muscles do their work, they obtain energy from glucose stored in the muscle cells as glycogen. When these supplies of glycogen run low, glucose from the bloodstream is used as an energy source. After exercise, the body replenishes the stores of glycogen in the muscle cells and liver, which further lowers blood glucose levels.
If you perform regular physical activity, and experience lows, a CGM system can help you figure out when exactly the lows begin, and how long they last. This way, you can take action before or during exercise sessions to compensate for the drop in glucose levels, whether that would involve an adjustment to your insulin injections, or a snack adjustment before or after exercise.
Similarly, a CGM system can help you figure out exactly how high your glucose level rises after eating. Checking your CGM data after meals, especially for the first one to two hours, can show you both the timing and the severity of post-meal glucose spikes. If you also keep a logbook of the foods you eat, you can figure out which foods make your glucose levels rise the most, and take action accordingly. That may mean, for example, lowering the amount of carbohydrate-containing foods you eat during a meal; or, if you take insulin, adjusting your bolus dose accordingly.
Continuous glucose monitoring system studies and A1C levels
A number of studies have shown that real-time CGM has a positive effect on blood glucose and A1C levels.
Dr. Robert Vigersky and colleagues studied a group of 100 patients with type 2 diabetes, to determine whether CGM had an effect on glucose levels. At the end of the study the participants who used CGM (vs. self-monitoring of blood glucose only) had much greater decline in A1C levels, in some cases by as much a 1%.
Dr. Hye Jin Yoo and colleagues studied 65 patients with poorly controlled type 2 diabetes over a period of three months. The people in the study who used a CGM system had lower glucose and A1C levels than those who didn’t use the CGM system; as well, they also had a reduction in body weight.