There are now three types of continuous glucose monitors available. They all transmit glucose results wirelessly from a small sensor placed just beneath the skin via a transmitter whose signal is received by the monitor placed anywhere from 5 to 10 feet away. Results are sent from every minute to every 5 minutes and the trend of the readings can be shown on graphs. One, the Medtronic Realtime System®, can transmit the results into the same unit that is used as the insulin pump.
However, even though the same unit acts as both monitor and pump, it is still necessary for the wearer to pro-gram and set the amount of insulin to be delivered. Studies have shown that the additional information provided by the frequently delivered values and the graphed trends reduces high and low glucose events in the wearer by about half.
It is important to note that all the current continuous glucose monitors are approved only for use with and alongside conventional glucose meters. This means that before acting on the information the continuous monitor provides, you should verify it by obtaining a reading with your regular monitor.
Also, the two technologies provide similar but slightly different information. The conventional monitor measures blood glucose from the blood droplet resulting from the finger prick. The continuous meter does not use blood. Instead, it measures the glucose level in the fluid bathing the tissue under the skin. This is in fact derived from the blood plasma itself, but it takes several minutes to adjust to reflect the blood level.
The avail-able continuous meters need to be calibrated twice daily (Medtronic Guardian®, Dexcom 7®) with a conven-tional fingerstick reading, although the newer Abbott Freestyle Navigator® needs only four calibration readings in a 5-day period. Once introduced, the sensor/transmitter can be worn for 3 (Guardian), 5 (Navigator), or 7 (Dex-com-7) days before the sensor must be changed.
The decision as to whether to get one of these monitors depends on the value to the wearer of knowing his or her readings on a minute-by-minute basis. For people early in the course of diabetes, on oral medications, and in good control, they are probably not necessary.
For people on insulin, with a history of low and high readings, especially if they are hard to predict or explain, the information provided by continuous glucose sensing may be very valuable. However, approval for insurance coverage is often limited to specific circumstances, such as the frequent occurrence of very high or low blood sugars that cannot otherwise be prevented.