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Continuous Glucose Monitor

How Do I Know if I Need One?


Updated July 11, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

It's never easy when a spouse gives you bad news about one of your patients. Last week, I was approached by the wife of one of my patients - she was in tears because her husband experienced a hypoglycemic (low blood sugar) episode that caused him to crash his car and be sent to the hospital. Thankfully, he is ok, but everyone is still in shock. This gentleman has several medical issues, including Type 2 diabetes. Because he deals with hypoglycemia so often, I suggested that he use a continuous glucose monitor (CGM). CGM is a portable device that includes a sensor, transmitter and receiver, which measures hundreds of blood sugars per day about every five minutes. CGM's help to trend blood sugar rises and falls and can alert a person with diabetes when a blood sugar is dropping or rising too rapidly. In addition, CGM's allow users to set targets or thresholds for high and low blood glucose numbers. Once the blood sugar rises or falls above the set range, the device will alert you. CGM's also sound an alarm if the rate of increase or decrease is very fast. While CGM's are wonderful tools for blood glucose management, they don't replace testing your blood sugar manually altogether. In fact, it is recommended that CGM's be calibrated with 3-4 finger sticks per day. As opposed to measuring the glucose in your blood, continuous glucose monitors measure the glucose levels in the interstitual fluid under the skin which can affect accuracy slightly. Continuous glucose monitors are not meant to replace blood glucose monitoring rather to act as an adjunct. In this patient's situation a CGM could have prevented an accident. 

Who Should Use a CGM? 

Persons with Type 1,Type 2 diabetes or gestational diabetes who require regulation of blood glucose because of: 

  • Acute episodes of hypoglycemia, ketoacidosis or hyperosmolar coma and other complications
  • Persons who switch from conventional insulin to pump therapy
  • Persons with extreme fluctuations in blood sugars and sustained elevated Hgba1c
  • Persons with hypoglycemia unawareness
  • Persons who experience hypoglycemia unawareness, especially in the evening hours

How Does it Work Exactly?

The tiny sensor is inserted subcutaneously under the skin using an inserter device. The needle used to insert the sensor does not remain in the skin for the life of the sensor - it retracts when the sensor is in place and is discarded. Most sensors can stay in place for about three to seven days and then must be replaced.The sensor measures interstitual fluid.  A transmitter sends information about glucose levels via wireless radio frequency from the sensor to a wireless monitor (about the size of a pager). A computer is needed to download, analyze and print data. 

I Thought CGM's Were Only for People with Type 1 Diabetes: 

Although many people with Type 1 diabetes use CGM's to enable better blood glucose control, CGM's can also be advantageous for people with Type 2 diabetes. This is especially true for people who have frequent low or high blood sugars and can't figure out why. And most importantly for those patients on insulin or other hypoglycemic agents that cannot recognize symptoms of low blood sugar, CGM's can be of great value as alarms can save lives. 

What are the Difference's Among CGM's on the Market? 

CGM's offer mostly the same functions with a few different components including sensor duration, range, meter interaction, pump interaction and there intended use. 

Sensor duration: refers to how long you can keep the sensor on before changing it, usually ranging between three to seven days. 

Range: refers to how far away you can be from the sensor to obtain information onto the receiver. If you are "out of range" from your receiver your information will not be transmitted. 

Meter interaction: In order to calibrate a sensor you need to test your blood sugar a minimum of two times per day. Some CGM's have companion meters that allow for transfer of blood sugars between the two. Other CGM's require use of a connection cable to download information for a specific meter or entering blood sugars manually. 

Use for Real Time vs. Diagnostic: Some CGM's are meant for diagnostic use by health professionals only. For example, the i-Pro is meant to be worn for three days, during this time the person wearing it is not aware of the glucose levels until the information is downloaded. Other CGM's are meant for patient use to provide real time blood glucose readings which can help people prevent and treat high and low blood sugars. 

For more information on specifics of CGM's on the market go to: http://www.diabetesforecast.org/2014/Jan/images/continuous-glucose-monitors.pdf

How Do I get a CGM?

Continuous glucose monitors are available by prescription. Ask your primary physician or endocrinologist if you are eligible for one. 


Continuous Glucose Monitoring. National Diabetes Information Clearinghouse. Accessed on-line, March 20, 2014: http://diabetes.niddk.nih.gov/dm/pubs/glucosemonitor/

Harrell, R & Orzek, E. AACE Position Statement: Coding for Continous Glucose Monitoring. Accessed on-line, March 20, 2014: https://www.aace.com/files/position-statements/cgmpositionstatement.pdf

Diabetes Forecaste. Consumer Guide: Continous Glucose Monitors. Accessed on-line, March 20, 2014: http://www.diabetesforecast.org/2014/Jan/images/continuous-glucose-monitors.pdf



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