Johns Hopkins Diabetes GuideDevices

Continuous Glucose Monitors

Susan Renda, DNP, Clare J. Lee, M.D., Thomas Donner, M.D.
Continuous Glucose Monitors is a topic covered in the Johns Hopkins Diabetes Guide.

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  • Continuous glucose monitors (CGM) are devices that can measure interstitial glucose every few minutes to inform real-time glycemic values and trends to the user.
  • CGM devices consist of three parts, a sensor, transmitter, and receiver. The sensor is inserted under the skin to check glucose levels in the interstitial fluid and transmits within 3-20 feet of a receiver. The sensor stays in place for several days to a week after which it must be replaced.
  • The receiver displays glucose values in real-time and can recall graphs of trends over the past 1-24 hours.
  • Alarms can be set on the device to detect and warn the user of upper and lower glucose levels. As well, the rate of change in mg/dl/min can be set to alarm if the user experiences rapid changes in glucose.
  • Sensors and transmitters are waterproof from 3-8 foot depths for 30 minutes to 24 hours, thus allowing for bathing and swimming.
  • Receiver batteries require recharging approximately every 14 days.
  • The user must calibrate CGM by checking blood samples at least twice a day using a blood glucose meter.
  • CGM devices must be removed before magnetic resonance imaging or computed tomography, as they can be damaged from these radiological studies.
  • Use of acetaminophen while wearing the sensor from DexCom may falsely raise the sensor glucose readings.
  • CGM devices are safe to be worn on U.S. commercial airlines. For Medtronic Guardian CGM, the transmitter should be disconnected from the sensor while on an aircraft.
  • Information can be shared to an application (app), to another person via their smart phone, and to an office practice. The receiver can be downloaded at an office visit for review of results and trends.

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Last updated: August 2, 2017