CGM devices

Although the potential for miniature electronic devices to measure glucose levels was recognized by the early 1960s, the first CGM device was not approved until 1999.6 There are currently three FDA-approved CGM devices available in the United States. Comparative studies have not been done to determine whether one of the approved devices is more accurate than the others.

All three are equipped with hypoglycemia and hyperglycemia alarm systems.1 All approved CGM devices use minimally invasive, very thin disposable sensors that are inserted under the skin of the upper arm or the abdomen with an applicator. Glucose oxidase-coated electrodes measure glucose concentrations in interstitial fluid, and the receiver/display unit calculates equivalent blood glucose levels. The enzyme reacts with glucose to produce hydrogen peroxide, releasing energy in the form of an electrical current that reflects glucose concentrations on the electrodes.1

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Abbott Freestyle Navigator

Approved by the FDA in 2008, the Abbott Diabetes Care Freestyle Navigator reports glucose concentrations more frequently than the earlier-approved devices described below. The Navigator indicates glucose readings every minute, whereas the other devices shown in Table 1 report glucose concentrations every five minutes. Sensors last up to three days. The maximum receiver range is 10 feet.1 Current glucose levels and trend information are displayed, but rather than a line graph display of trend data, trends are represented by an arrow pointing up or down. Sensors require only a single blood-based calibration during their three-day life span, according to the manufacturer.1

DexCom Short-Term System

Approved in 2007, this CGM device has a seven-day sensor life span. The sensor is placed beneath the skin of the patient’s abdomen. It requires fewer daily blood sample calibrations (two) than the MiniMed Guardian.

Medtronic MiniMed Guardian and iPro Recorder

The Medtronic MiniMed Guardian, approved by the FDA in 2006, displays the current (most recently measured) glucose values and a trend graph of recent measurements.1,6 The sensor is placed in the patient’s arm and measures interstitial fluid glucose concentrations every five minutes. Calibrations using finger-stick blood samples are required up to four times per day.1 The receiver/monitor must be placed within six feet of the patient.1

The Guardian has a reported error rate of 21.3% compared with blood-based patient self-monitoring, with only a 63% hyperglycemic-event sensitivity.8 The reported false-alarm rate is 19%.8 The reported hypoglycemia-alarm sensitivity is 67% and false-alarm rate is 47%.8 Despite poor sensitivity, the alarm function does appear to reduce the duration of hypoglycemic events.1

The Medtronic iPro Recorder was approved in 2008 for clinician-only use and cannot be purchased by patients.1 The device is worn for three days to record glucose data for treatment strategy planning. The iPro Recorder does not come with a monitor display because it is not approved for patient use. Data stored on the iPro is downloaded at the office during a follow-up visit for use by the clinician.

Mr. Furlow is a medical writer and health-care journalist in Albuquerque, N.M.


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