The DexCom, Medtronic MiniMed, and Abbott Pharmaceutical (not yet available) systems all work in a similar way. The sensor is a tiny flexible probe that you insert under the skin in the same way you insert an insulin pump infusion set can-nula (see Chapter 6). The sensor measures the glucose concentration in the tissue fluid every five minutes for about three to seven days before it needs replacing. All the systems have software available to download the data into your computer.
These systems are not covered by insurance, and the initial cost for the two systems that are currently available is about $800 to $1,000. The main expense, however, is the sensor, which has to be changed every three to seven days. The three-day sensor costs about $35. This adds up to an out-of-pocket expense of about $4,000 annually.
These systems enable some patients to improve control without increasing the risk of hypoglycemia. The individual blood glucose values are not that critical; what matters is that the system alerts you to the direction and the rate at which the glucose level is changing, allowing you to take corrective action. You learn how different foods get absorbed and how quickly your glucose rises after a meal. You can use this information to change the timing and the ratio of insulin for carbohydrates to control the glucose rise. The other main benefit is in alerting you to low glucose levels. Spouses and friends report that they especially appreciate the low glucose alerts.
With the DexCom system, the measured glucose values are transmitted to a separate pager-like device with a screen, with alerts for low and high values. The screen of the DexCom device graphically displays the glucose levels for the previous nine hours. It also displays the last glucose number.
With the MiniMed system, you have the option of having the data wirelessly transmitted to the screen of an insulin pump, again with alerts for high and low values. This system graphically displays the glucose levels for the previous twenty-four hours and the last glucose value. Unlike the DexCom system, the MiniMed system also allows you to scroll back to see actual numbers for previous glucose levels rather than just a graphic display.
Both the DexCom and MiniMed systems require you to calibrate the machines with periodic finger-prick glucose levels. There are concerns regarding reliability of the values, and so you do need to check your blood glucose with your home blood glucose monitor before making interventions such as injecting extra insulin or eating extra carbohydrates.
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