The Continuous Glucose Monitoring System: "What you don't know can hurt you."
Report from the meeting of the American Association of Clinical Endocrinology
We have entered a new era in diabetes care! Recently, some endocrinologists have reported the results of data from the Medtronic MiniMed continuous glucose monitoring system (CGMS). While this device currently does not provide the user with a continuous readout of blood glucose levels, it does the next best thing. When downloaded into your endocrinologist's computer, it provides three days of information useful in identifying problems and adjusting treatment programs. Several studies have shown that this does lead to improvements in overall blood glucose control (lower HbA1c values and fewer hypoglycemic events).
You probably are checking blood sugar levels several times a day. While this information is important in making gross adjustments in your treatment plan, 3 or 4 blood sugars is now shown to be insufficient in fine-tuning. When blood sugar is checked intermittently, what is seen is only a few points in time. And it is impossible to tell from a single number if the level is rising or falling, and therefore there is a fifty-fifty chance that the wrong decision will be made about what to do.
The sensor provides a true picture of glucose control. It averages interstitial fluid (ISF) glucose levels every five minutes. Therefore, when data are printed out, you see a graphic representation of what was going on during the monitored period. This information can be used to identify problems, and fine-tune the insulin, meals, and exercise program. For example, in one study, the fluctuations occurred in greater frequency than expected; the excursions lasted longer than had been thought; and there was unrecognized hypoglycemia and hyperglycemia. Most of the unrecognized hypoglycemia occurred during the night, and most of the hyperglycemia occurred three or more hours after meals (especially after a high-fat meal like pizza!).
How does it work?
A small sterile disposable glucose-sensing device called a sensor is inserted into the subcutaneous tissues, using the same procedure as when inserting the needle on the end of the catheter used with insulin pumps. This sensor measures the change in glucose in ISF, and sends the information to a beeper-sized black box (called a monitor) which stores the results for three or four days. The monitor must be calibrated daily by entering at least three blood glucose readings obtained at different times, using a standard blood glucose meter. You will also be expected to enter insulin doses, exercise, and meal information into both a logbook and the monitor. After three days, the monitor is taken back to your endocrinologist's office, where it is placed in a docking station, which is connected to a standard personal computer. Specialized software then downloads the stored information, so that you and your diabetes team can review the data and decide on a treatment plan aimed at correcting any problems. Later, repeated CGMS testing and followup HgbA1c levels can be done to see whether the changes worked.
The Impact of CGMS
For the first time we can see what happens to glucose levels on a minute-to-minute basis, and evaluate trends, during normal daily activities. We expect that the availability of CGMS dramatic impact on the way diabetes is treated.
Contact your diabetes team to inquire about CGMS availability in your area. More information can be found on-line at Medtronic MiniMed's website, at Continuous Glucose Monitoring System.
Posted 14 April 2000
Updated 25 August 2002
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