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Continuous Glucose Monitoring:
A Movie is Worth a Thousand Pictures
A Review of the Medtronic Guardian REAL-time system

by Thomas Ley


The Medtronic Guardian® REAL-Time CGMSThe expression “information is power” is especially true for diabetics seeking tight blood glucose control using either multiple daily injections of insulin (MDI) or insulin pumps. Using these therapies, you can decide how much short-acting insulin to take four, six, eight, or even more times per day, based upon the corresponding four or six or eight blood glucose readings you take using finger sticks.

Imagine how much blood glucose readings might improve if your blood glucose was automatically measured and displayed every five minutes, 24 hours a day, seven days a week. Well, you don’t need to imagine it, it is here, and is known as a continuous glucose monitoring system, or CGMS.

Medtronic is one of a small handful of companies offering a continuous glucose monitoring system, and they recently released their latest product, the Medtronic Guardian® REAL-Time CGMS. With the Guardian REAL-Time, you can follow the trend of your blood glucose up and down throughout the day and night in response to different foods, exercise, and insulin doses. Knowing what direction blood glucose is trending can be at least as important, if not more important, than knowing your current blood glucose reading. As Gary Fox of Med-tronic says “the biggest advantage is the education you get from the Guardian REAL-Time regarding how different foods, stress and other activities impact your blood sugar.”

The data obtained from CGMS can be compared to watching a movie of blood glucose readings throughout the day, whereas the data from finger sticks taken four or six times a day is like viewing individual snapshots. A single snapshot may be misleading if what occurred prior to the picture is not known. For instance, if you are getting ready for bed and discover that your blood glucose is 88, you might often choose to eat a small snack. However, what if you knew from your CGMS that an hour ago your blood glucose was 72 and a half an hour ago it was 79? Knowing this, your current reading of 88 is not worrisome at all.

How does the Guardian REAL-Time work?
Three small but separate pieces make up the Guardian REAL-Time CGMS. The first piece is the blood glucose sensor which is inserted under your skin just like an insulin pump delivery site. It measures the level of glucose in your interstitial fluid every ten seconds and produces an average of these readings every five minutes. The sensor is disposable; it remains under your skin for up to three days and must be replaced. The portion that is visible above your skin is about the size of a dime. Each sensor costs $35.

The second piece in the system is the new MiniLink™ transmitter. This piece connects to the sensor and is about the size of a quarter. When connected to the sensor, the two pieces become a single unit which is waterproof. The MiniLink™ transmits the blood glucose readings to the Guardian REAL-Time monitor wirelessly; no cords or wires to have to connect, disconnect or get tangled. The transmitter is rechargeable (in only 20 minutes) and will last for one year before it must be replaced.

The final piece in the system is the Guardian® REAL-Time monitor. This device is exactly the same size and shape as the Medtronic series of Paradigm® insulin pumps. It continuously displays your current blood glucose reading received from the MiniLink™ transmitter along with a trend arrow to show whether your blood glucose is rising or falling. The monitor has three different types of configurable alarms, which go off at a pre-set level for either a high or low blood glucose reading (the alarm sounds different for a low as opposed to a high). You can set the alarm to warn you when your blood glucose is changing rapidly in either direction. Finally, the monitor can alert you up to thirty minutes prior to when it predicts that, based upon the trend and the rate of change, your blood glucose will reach the pre-set high or low level.

You should not base insulin dosing exclusively on the blood glucose reading provided by a CGMS. CGM systems do not eliminate finger sticks; you must still take one twice a day and enter the value into the Guardian® REAL-Time monitor for calibration. You can also enter into the monitor data such as the time of and carbs in each meal or snack, the type and amount of exercise you do and the type and amount of each insulin dose, which may help your doctor make better treatment decisions. You can download all this data to a PC and upload to the Medtronic Web-based CareLink™ personal software. Here, you or your doctor can view graphs of trends that will highlight areas for improved diabetes care.

The Guardian REAL-Time system is not accessible for people who cannot rely upon sight to read and enter data into the monitor. Unfortunately, practically no insurance coverage is available for CGM systems yet. The Guardian REAL-Time starter kit costs around $1,300 and includes four sensors, the Mini-Link™ transmitter and the Guardian® REAL-Time monitor. The CareLink™ software is included.

Look for an article in an upcoming edition of Voice of the Diabetic which outlines all CGM systems currently on the market or undergoing the FDA approval process. You may visit for more information on the Guardian® REAL-Time CGMS or you may call 1-800-MINIMED (646-4633). Alternatively, you may write to: Medtronic Diabetes c/o Customer Support
18000 Devonshire Street, Northridge, CA 91325-1219

Tom LeyAbout the Author
Tom Ley has had Type 1 diabetes since he was seven and has been blind since he was 17. He is a manager and senior software support analyst for UPS and has a strong background in the field of accessible technology for the blind. He is the technology writer for the Voice of the Diabetic.