Continuous glucose monitoring (CGM)

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Dr. Dennis Van Hoof, PhD, CLC

“A1c does not show your ups and downs.


Continuous glucose monitoring (CGM)

Keeping your blood glucose as close as possible to normal levels (normoglycemia; see Blog post “Blood glucose“) is a non-stop challenge that all diabetics are dealing with every day, hour to hour, minute to minute. Besides food and physical activities, almost everything else you do affects your blood glucose level, which makes proper blood glucose control a serious ordeal. The hazards of deviating too much from those normal values are well-known: too low (hypoglycemia) and you face the immediate danger of a coma, too high (hyperglycemia) and you risk developing diabetes-associated complications.

“Normal blood glucose levels fluctuate between 72 and 100 mg/dL when fasting, and stay below 140 mg/dL after a meal.”

Results from long-term studies are slowly trickling in, but it is not yet clear what is more damaging in the long run: continuous hyperglycemia (too high blood glucose) or hypoglycemia (too low blood glucose), or maybe the wild ups and downs that deviate way too much from normoglycemia (the average healthy range). What is clear, is that keeping your blood glucose within the upper and lower limits of normoglycemia as much as possible is the best. But how do you know if you are doing it right? What is a good way to keep track of your daily fluctuations, so that you can better adjust and optimize your treatment strategy?

Ames meter

The Ames Reflectance Meter was one of the first blood glucose meters. [source]

Snap-shot blood glucose measurement — In order to stay within the “safe zone,” you need to anticipate how the things you eat and do will affect your blood glucose, and also know when to correct for hyperglycemia (with extra insulin or physical activity) and hypoglycemia (with sugary foods/drinks). The first blood glucose meter was developed in the early 1960s, but it took another 20 years before the first home-glucose meters became available to the general public. Those “finger-prick” meters, which are still the most popular today, use tiny blood droplet from your finger to measure the concentration of glucose circulating in your blood at that particular moment.

OneTouch Ultra

The OneTouch Ultra2 is a modern-day blood glucose meter.

The disadvantage of these “snap-shot” measurements is that you don’t know what your value was an hour ago, and where it is headed. Let’s say you measure the following blood glucose values:

  • 1:15 am = 99 mg/dL
  • 10:00 am = 102 mg/dL
  • 3:20 pm = 98 mg/dL
  • 6:20 pm = 101 mg/dL
  • 11:10 pm = 94 mg/dL

You may believe that your blood glucose values are perfect, but you don’t know what went on in between those measurements. You could completely miss the high and low values, as you can see in the example below, where the actual blood glucose trend is shown during that day.


When taking snap-shot measurements at random time points (indicated with the 5 blue circles), you may think that your blood glucose is perfectly within the healthy range, while in reality, it was too high (indicated in yellow) and too low (indicated in red) on several occasions.

Continuous glucose monitoring — Since a few years, continuous glucose monitors (CGMs) are becoming more popular, and for good reason. They automatically take a glucose measurement every few minutes, giving you a good idea of how your levels fluctuate throughout the day, so you can make adjustments to your eating habits, timing of insulin administration and physical activities.

Dexcom dots

This Dexcom CGM automatically takes a glucose measurement every 5 minutes. Each dot in between the upper yellow and lower red line is a measurement.

The catch is that CGMs do not measure blood glucose, but interstitial fluid. While a finger-prick measurement uses a tiny blood droplet from your finger, CGMs have a sensor that is inserted underneath your skin. It stays there for several days, taking an automatic measurement every few minutes. This sensor is not directly in touch with blood, but the fluid in between your cells; this is the interstitial fluid. Glucose is constantly moving out of your blood vessels into this fluid to reach your cells that need the glucose for energy. But the glucose concentration in this interstitial fluid is always lagging behind the actual value in your blood.

“CGM does not measure blood glucose.”

Although not perfect, CGMs are the as good as it gets right now. They have allowed countless diabetics to improve their A1c (see Blog post “Hemoglobin A1c“), minimize the chance of developing long-term complications from constant hyperglycemia, and give timely alerts before hypoglycemia may occur. They have become an essential element in supporting a healthy and active lifestyle for excellent diabetes management .

If you want to learn more about a healthy and active lifestyle, without diets and restrictions or limitations, then follow me on social media like Facebook, LinkedIn and Instagram.

Also check out my website, and consider signing up for the personal diabetic lifestyle coaching or one of the online group workshops that I offer through video conference.

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Keep an eye out for my next blog, and I hope to see you soon to get you started on the journey to your new life!

—  Dennis


Dr. Dennis Van Hoof is a Certified Life Coach (CLC) with an academic PhD degree in Biochemical Physiology. By combining 20 years of first-hand personal diabetes experience with his in-depth scientific background, he developed a method to efficiently manage his own diabetes in a sustainable way. To learn how you can do this too, reach out for personal Diabetic Lifestyle Coaching or follow a group workshop that is specifically tailored to people with Type 1 or 2 Diabetes as well as pre-Diabetics and those at risk due to being overweight or obese. His clients thrive with their challenges and become an inspiration™ to others — with or without diabetes.

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