How do continuous blood glucose monitors CGMs) work?

Updated: Jan 22, 2020
  • Author: Benjamin Daniel Liess, MD; Chief Editor: George T Griffing, MD  more...
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A continuous blood glucose monitor (CGM) assesses blood glucose levels on a near-continuous basis. A typical system consists of a glucose sensor placed subcutaneously, a nonimplanted transmitter, and a receiver worn like a pager, which records blood glucose levels at frequent intervals and monitors trends.

CGM systems monitor interstitial fluid glucose levels. They must be calibrated with traditional fingerstick tests. Before treatment of reported hypoglycemia or hyperglycemia with insulin, confirmation with a fingerstick test is recommended because of the 5- to 15-minute lag in data reporting.

Continuous monitoring provides documentation of blood glucose response to insulin dosing, eating, exercise, and additional influences. Overnight monitoring may identify problems with insulin dosing and allow adjustments of basal levels. Many units are equipped with alarms to warn patients of hyperglycemia or hypoglycemia and provide time for treatment. Studies have demonstrated that patients using CGMs experience fewer hyperglycemic episodes and may decrease their glycated hemoglobin (HbA1C) levels. [7, 8, 9]

One recent concern, however, is proper calibration and availability of control solutions at pharmacies and appropriate use by patients during calibration. Lack of adherence to proscribed methodologies of use may lead to erroneous data and thus possible mistreatment of diabetes by patients. [10] Future development and technological advancements aim to allow for improved sensors and calibration software, creating better systems designed to automate delivery of insulin partially (eg, low glucose suspend) or entirely (eg, “fully closed-loop” artificial pancreas). [11, 3, 5]

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