If you have difficult to control diabetes on insulin therapy—or if you’ve had troublesome drops in blood glucose—your health care provider may have suggested a continuous glucose monitor. This monitor can reveal minute-to-minute fluctuations in blood glucose.

The monitors are considered most appropriate for:

  • Persons with type 1 diabetes who have continued difficulty controlling their blood glucose and have Hb A1c levels higher than goal
  • Persons with diabetes on insulin therapy who have good A1c levels but may be at risk for low blood glucose levels particularly at night
  • Persons with diabetes who experience frequent drops in blood glucose or those who experience low blood glucose levels so often that they no longer notice the warning signs

These monitors are attached to a small sensor placed usually beneath the skin of the person’s abdomen, arm, or upper buttocks. On top of the skin sits a transmitter, which relays information to a wireless receiver.

Every 5 to 15 minutes, the sensor measures blood glucose levels. The transmitter sends the reading to a hand-held device known as a receiver, which resembles a pager however there may be a brief lag between glucose levels in the blood and sensor readings. The patient can see the results on the receiver’s screen, and download the information.

The monitors provide a huge amount of information but this information reflects the amount of glucose in the fluid just under the skin, rather than the amount of glucose in the blood. As a result, this means that the results are not as timely or accurate as home blood glucose test kits and there can be a small lag in the continuous glucose monitor readings.

Because of this, most monitors cannot serve as a replacement for regular home blood glucose testing. Most real-time continuous glucose monitor will need to be calibrated with results from a finger stick glucose reading multiple times throughout the day. However, a few recent CGMs do not necessarily require fingerstick blood glucose calibration or confirmation before making treatment decisions.

“Flash” or intermittent CGMs provide readings on demand by waving a receiver over a sensor that is usually worn on the arm. An implantable CGM is also now available.

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