What is continuous glucose monitoring?

Continuous Glucose Monitoring is a relatively new technology which allows a person to measure blood sugar levels in the human body every five minutes, twenty-four hours a day, and wirelessly transmit the data to a handheld device thus creating a maximum of 288 blood sugar checks each day.

Because the blood sugar checks are automated, alarms can also be set based on predefined thresholds for high and low levels which when exceeded alarm the user via an audible warning. Even while asleep, wearers of the CGMS can then be alerted to out of range blood sugar levels and take corrective action.

There are eight (8) parts to a CGMS:

1) Invasive sensor 2) Transmitter 3) Handheld device 4) PC or server-based management software 5) Cable for connecting spot check meter to CGMS handheld

   - DexCom only; the Medtronic device allows the user to manually enter spot check blood sugar data 

6) Spot check glucose meter 7) Spot check meter test strips 8) Spot check test strip control solution

Invasive sensor The two currently available systems are invasive meaning that they require the user to wear an explant which penetrates the skin leaving a flexible piece of metal coated with a chemical under the skin for up to several days. The sensor is made to stick to the skin and is replaced frequently. Longevity of the sensor depends on many factors.

Transmitter The invasive sensor is powered by an external transmitter affixed to the sensor and worn as a combined unit on the skin. The transmitter also transmits electrical pulses through the sensor and measures the returning signal which varies based on the level of glucose in the body's interstitial fluid. This measured signal is then transmitted externally via short range wireless to the patient's handheld device.

Handheld device The handheld device takes the raw signal(s) from the transmitter and translates these into blood glucose concentration data (mg/dL) in the same familiar units as the spot check blood glucose meter. This makes it easy for any person to understand the current blood sugar level of the person wearing the CGMS. wireless monitor has a screen that shows blood sugar trends on a graph over time, making it easy to see what is happening and where things are likely going. Thus, the CGM makes it much easier to make accurate adjustments and play the role of a pancreas.

 The system also requires calibration, involving at least two finger sticks per day. Calibration is required to maintain the accuracy of the sugar readings.

The portion of the sensor under the skin is in contact with interstitial fluid, not blood. Interstitial fluid sugar levels adjust approximately fifteen minutes after changes have occurred in blood sugar levels. So there is a small delay in the real-time accuracy of the system. But this issue does not interfere with the use of the Dexcom as a life-enhancing information tool and safety net.

Dexcom's CGM system is the first generation of a relatively new technology, and new technologies always have room for improvement. One problem with the Dexcom system involves the low blood sugar warning system. Because interstitial fluid sugar levels rise more slowly than blood sugar levels, the low blood sugar warning system is slow to adjust to corrections.