Continuous Glucose Monitoring Systems for Diabetes

Imagine yourself in an unfamiliar city. You need to get to a certain point, but the route is new to you. It seems someone verbally told you how to get there, but the streets are very narrow and winding, and you got lost. It’s a different story if you have a navigator that will open the entire city map and explain in detail how to reach your destination by the shortest route, avoiding traffic jams.

This often happens with glycemia as well, when those single blood glucose measurements with a glucometer, in terms of time in a day, cannot show the true picture of glycemia. There are situations related to different life periods, acute illnesses, physical activities—so-called “sugar spikes”—where it’s difficult to navigate even for patients with long-standing diabetes and experienced doctors. Confusion arises, and it’s unclear what to do—increase medication dosage or decrease it.

The incidence of diabetes is steadily increasing. However, over the past 50 years, there has been a breakthrough in diabetes treatment, with many highly effective medications becoming available. Despite modern advances, a significant portion of people with diabetes (DM) do not achieve target glycemic levels, leading to an increase in acute and chronic complications, significantly reducing quality of life and leading to disability. Chronic hyperglycemia, i.e., high blood sugar, as well as pronounced fluctuations in glycemic levels throughout the day, “sugar spikes,” play a leading role in their development  – i.e., glycemic variability

According to the largest global studies, glycemic control is of paramount importance in the treatment of diabetes.

Continuous glucose monitoring has revolutionized the lives of patients and doctors. It’s as if our eyes have been opened to situations that were previously beyond understanding. Today, providing personalized therapy selection, especially for patients on insulin therapy, is very difficult without this data.  This is a completely different level of glycemic control and correction, providing not only a complete picture of glycemia but also allowing remote transmission of information to the doctor and addressing therapy adjustments.

Look at this picture, where seemingly perfect blood glucose levels taken from a finger are recorded. And compare it with what actually happens a couple of minutes later according to continuous glucose monitoring data.

Continuous Glucose Monitoring Application

• helps identify hidden abnormalities, such as frequent cases of hypoglycemia (low blood glucose levels)
• will allow for a clear understanding of the nature of the glycemic curve throughout the day and over an extended period
• identify all issues on the path to diabetes compensation (insulin resistance, chronic insulin overdose – the so-called Somogyi syndrome, the “dawn phenomenon” and “dusk phenomenon,” “early breakfast phenomenon,” unclear hypoglycemia, unclear hyperglycemia)
• will help adjust glucose-lowering therapy (both insulin therapy and oral medication) considering individual characteristics;
• select and program the necessary insulin administration program;
• considering the duration of use (6-14 days), the system allows for the establishment of trends in glycemic changes and the identification of errors in treatment and insulin administration;
• allows understanding how certain products affect glycemic levels, which will help in selecting the right diet
• will allow you to understand how different types of physical activity affect glucose levels in the body, which will help in sports activities

Thus, for the first time, both the patient and the doctor have the opportunity to obtain a complete picture of blood glucose level fluctuations.

Who can particularly benefit from the use of 24-hour monitoring

• patients with type 1 diabetes or type 2 diabetes on insulin therapy;
• pregnant women;
• patients who have not reached target values HbA1 or another individual target indicator;
• in the presence of severe hypoglycemia (≥1 time in the past year)
• with frequent episodes of mild hypoglycemia (≥1 time per day)
• in case of impaired hypoglycemia recognition
• with high glycemic variability, regardless of the level of H bA1c;
• when the time in the target glucose range is less than 50% according to CGM data in “blind” mode
• to any patient, on any therapy, if they wish to conduct regular self-monitoring of glycemia and follow the recommendations of the attending physician

The continuous glucose monitoring system consists of devices that measure sugar in the interstitial fluid at regular short intervals (1–10 minutes) over several days (6-14 days)  Interstitial fluid is a thin layer of fluid surrounding cells under the skin, where glucose freely diffuses from the capillaries. Glucose levels in interstitial fluid are similar to those in capillary blood, allowing the use of widely accepted standards for diabetes treatment.

Any continuous glucose monitoring system consists of three main parts: sensitive sensor, monitor, and data transmission device .
The principle of operation for most devices used is similar. A platinum sensor in a silicone sheath, impregnated with the enzyme glucose oxidase necessary for the enzymatic breakdown of glucose in the interstitial fluid of subcutaneous fat, is installed in the patient’s subcutaneous tissue. Measurement occurs through a two-step chemical reaction, during which a glucose molecule donates 2 electrons, creating an electric current, and the device for continuous glucose monitoring measures the current strength, but the result is displayed in millimoles per liter. The higher the glucose content in the interstitial fluid, the more electrons are produced, and consequently, the higher the electrical potential. This method of measuring glucose levels is called electrochemical. This same method is used in most modern glucometers.
Depending on the manufacturing technology, sensors may vary in sensitivity and accuracy, lifespan, selectivity, etc. An analyzer is connected to the sensor, which can either record and store information or transmit it via radio to a reading device for real-time display.
Devices for CGM measure glucose levels in interstitial fluid, which may lag behind changes in blood glucose levels measured by a glucometer by 5-15 minutes, especially in cases of rapid rise or fall in blood glucose concentration. This delay is due to three factors:
–  physiological delay time and is associated with the time of blood flow to the skin
–  sensor response time to glucose intake;
– signal processing time by the sensor
This necessitates calibration with blood glucose level measurement twice a day by most CGM devices. It is better to perform calibration when the glucose level is relatively stable (i.e., before meals, before physical activity, before administering bolus insulin).

Currently available NMG systems can be divided into three categories:

1) Continuous Glucose Monitoring (CGM) in “blind” mode or so-called professional CGM. Used in medical facilities.

2) Real-time HMG reflecting current glucose levels

3) Periodically scanned/intermittently viewed continuous glucose monitoring (CGM) or flash glucose monitoring (FGM).

The greatest interest lies in real-time continuous glucose monitoring and flash glucose monitoring. The main difference between flash monitoring and real-time continuous monitoring is in the way the sensor processes and transmits information.

• Continuous monitoring transmits readings from the sensor to the receiver (smartphone, pump) in real-time via BlueTooth or NFC. This happens automatically, no actions are required from the patient.
• Flash monitoring (Freestyle Libre 1 and 2 generations) cannot do this. To get current readings, the user needs to take action: apply the scanner to the sensor. Although modern technologies allow flash monitoring to be turned into continuous monitoring. But more on that in another article.

There are many devices for self-monitoring of glycemia and glucose monitoring in the world. In Russia, devices for continuous glucose monitoring (CGM) by the company are certified   MEDTRONIC  and flash monitoring FreeStyle Libre Abbott.

Read about the features of each system in the following articles.

Endocrinologist Dr. Hakimova Gulnaz Albertovna