It is not possible to perform SMBG frequently enough to accurately identify all major BG excursions. Real-time glucose sensors, also called CGM systems, measure the concentration of glucose in blood and/or interstitial tissue fluid every 1-5 min. Currently available sensors are inserted into the subcutaneous tissue and measure glucose in the tissue fluid for 3 to 7 days. The implanted sensor must be calibrated to a finger-stick SMBG, and recalibrated two or more times per day, to make sure the sensor output signal accurately reflect the BG concentration.
The BG trend data provides a real-time appreciation of the glucose direction of change (increasing or decreasing); and the glucose rate of change (± 0.5, ± 1.0, ± 1.5, ± 2.0, ± 2.5, ± 3.0mg/dL/min) (Fig. 1). CGM systems display two up-arrows or an arrow that moves from 3 o'clock to 12 o'clock to denote a rapidly rising glucose level. Two down-arrows or an arrow that moves from 3 o'clock to 6 o'clock denotes a rapidly falling glucose level. The displayed trend data can be used by the patient, physician and diabetes educator to enhance BG control through a better understanding of the relationship between meals, exercise and sleep with the amount/timing of insulin and oral hypoglycemic drug therapy (Fig. 2A- 2C) (17-23).
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