What Is a Continuous Glucose Monitoring System (CGM) and How Does it Work?

What Is a Continuous Glucose Monitoring System (CGM) and How Does it Work?

A Continuous Glucose Monitor (CGM) is a device worn on the body that monitors glucose levels continuously throughout the day and night1. It is becoming a popular option for people with diabetes to monitor their blood sugars instead of using a blood glucose meter and fingersticks. The system consists of three components, a sensor, transmitter, and receiver.2,3 

  • Sensor: Placed under the skin, usually on the abdomen or arm, using an inserter device. The sensor reads the glucose levels.  

  • Transmitter: Connects to the sensor and wirelessly sends the sensor data to a receiver every few minutes.  

  • Receiver: Displays data including the glucose reading, the direction of the reading (increasing, decreasing or stable), and sensor graphs. It is a separate device, either provided by the CGM company or an app on a personal device such as a compatible smartphone. It can also be used to set alerts so the user is notified when glucose levels are going too high or too low.  

CGMs have evolved over the last twenty years and have become more accurate, smaller, easier to insert, and are now integrated with some insulin delivery devices such as a smart insulin pen or an insulin pump. CGMs measure glucose levels in interstitial fluid around cells, which correlates well with blood glucose. The American Diabetes Association (ADA), recommends that, when used properly CGM is a useful diabetes management tool for people with diabetes who take insulin with multiple daily injections or use insulin pump therapy.1 The ADA standards reinforce the importance that people with diabetes who use CGM receive education, training, and support to optimize the value of a CGM.1   

Professional CGMs are systems used by diabetes care clinicians who place them on people with diabetes for usually 7 – 14 days. The data is then used to assess glucose patterns and trends to make diabetes management decisions.1

Today most CGM systems are cleared by the FDA for use without the need to additionally check a blood glucose level with a meter to make diabetes management decisions. However, according to the ADA people using CGMs need to have the ability to do a blood glucose check to calibrate their CGM and/or verify CGM readings if they differ from the symptoms they are experiencing.1    

References
1: American Diabetes Association. 7. Diabetes Technology: Standards of Medical Care in Diabetes – 2021. Diabetes Care. 2021;44(Supp 1):S85-S99.
2: Spicer-Moore S. Integrating continuous glucose monitoring into your practice. Diabetes Dietetic Practice Group - On the Cutting Edge. 2019;40(4):3-7.
3: Campbell A. Continuous glucose monitoring updates. diabetes self-management. https://www.diabetesselfmanagement.com/education/continuous-glucose-monitoring-updates/. Accessed August 18, 2021.

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