Continuous Glucose Monitoring Systems

As the name implies, a continuous glucose monitoring system (CGMS) is a device that takes a glucose reading every few seconds over a period of days. By compiling glucose readings, calculating averages, and identifying trends, it can help the wearer gain valuable ongoing insight to diabetes control. The device also has lower and upper limit alarms that can warn the user of hypoglycemia or hyperglycemia. A CGMS is designed to supplement — and not to replace — regular self-monitoring of blood glucose. These devices require regular calibration with finger stick testing.

As of early 2008, three FDA-approved CGMS products — the Dex-Com Seven (DexCom), the FreeStyle Navigator (Abbott Diabetes Care), and the Guardian Real-Time (Medtronic Devices) were available on the U.S. market.

The FreeStyle Navigator (Abbott Diabetes Care) CGMS measures blood glucose levels each minute and transmits data wirelessly to its under-the-skin sensor, which must be changed every five days. It also has an “early warning alarm” that can be programmed to alert the wearer 10, 20, or 30 minutes before a high or low blood sugar event.

The Guardian REAL-Time CGMS (Medtronic Diabetes) measures glucose levels every five minutes for up to three days (when the sensor must be replaced). It consists of a sensor, which is inserted just under the skin; a transmitter that connects to the sensor; and a control module that stores and displays the blood glucose data. The sensor reads glucose levels in interstitial fluid, not in blood. Consequently, the values lag approximately 10 to 15 minutes behind blood glucose levels.

The testing data is sent wirelessly through the transmitter to the control module. The unit displays real-time glucose readings, alarms for preset blood sugar highs or lows, and graphs of blood glucose trends. Medtronic also manufactures the Paradigm REAL-Time CMGS for use with its Paradigm insulin pump. The system integrates the same REAL-Time continuous monitoring technology, but the transmitter wirelessly sends the data directly to the insulin pump.

Alert

Don't rely on a CGMS unit to detect a blood sugar low. CGMS measures glucose in interstitial fluid and the values it displays lag 10 to 15 minutes behind blood glucose values. Always use a finger stick test to detect and monitor treatment of a low.

The DexCom Seven (DexCom) is a CGMS that can be used continually for seven days before re-insertion of a new sensor is required. Like the Guardian, it consists of a sensor worn just under the skin, a wireless transmitter, and a unit for receiving, analyzing, and displaying the results. It also displays current readings, trend graphs, and alarms.

The FreeStyle Navigator (Abbott Diabetes Care) CGMS measures blood glucose levels each minute and transmits data wirelessly to its under-the-skin sensor, which must be changed every five days. It also has an “early warning alarm” that can be programmed to alert the wearer 10, 20, or 30 minutes before a high or low blood sugar event.

Noninvasive Testing Technologies

One minimally invasive continuous glucose monitoring device currently under development by SpectRx measures glucose levels in interstitial fluid (ISF). The SpectRx device uses a laser to create microscopic holes through which the ISF is collected. The ISF is then measured in a sensor patch.

Fact

The first FDA-approved noninvasive glucose meter was the GlucoWatch G2 Biographer. The product, a wristwatch-type device, measured glucose in fluid extracted from the skin via electrical current. Amid technical and regulatory issues, the product was sold to Animas in 2005, and that company discontinued the product in 2007.

Another product under development, the Symphony (Echo Therapeutics), features a transdermal (or on the skin) sensor to detect glucose levels. The Symphony is called a CTGM (continuous transdermal glucose monitoring) system and uses ultrasound technology to prepare the skin for the transdermal sensor. The device is currently in pilot studies.

Other technologies under development for both blood glucose testing and continuous glucose monitoring that don't involve lancing the skin include infrared, spectroscopy, and even contact lenses that measure the glucose in tears.

These and other new monitoring technologies that reduce patient discomfort and cost may help to increase testing compliance.

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