MiniMed Continuous Glucose Monitoring System Recommended by FDA Panel
MiniMed's Continuous Glucose Monitoring System (CGMS) is now available by prescription in the United States. The CGMS provides near continuous measurements of glucose levels for 72 hours, stores them, and can then be analyzed by your doctor. You do not see blood sugar readings while wearing the currently approved model.
Overview of the CGMS
The CGMS looks similar to an insulin pump and uses an implanted sensor, much like an insulin pump infusion set. An introducer needle is used to place the sensor in the subcutaneous tissue, usually, but not necessarily, in the abdomen. The introducer needle is then removed. Tape holds the sensor in place. After insertion, the sensor needs a one-hour stabilization period. At the end of the hour, the patient performs a finger-stick blood test and enters the results of the test into the meter. The meter uses the blood sugar value to verify that the sensor is working and to calibrate the results.
The CGMS is intended to be used for a three-day period, under prescription by a doctor. When in use, the CGMS measures glucose in the interstitial fluid every five minutes and stores that data for analysis by a personal computer after the three-day period. No information is provided to the patient during use. The patient must perform regular finger-stick blood tests and enter these blood sugar values into the CGMS. The blood sugar values are used to ensure that the implanted sensor is operating within specifications and to calibrate the sensor readings to blood sugar equivalents after use.
Why Would You Want the CGMS?
Since you still have to perform finger-stick blood tests, you might ask, "Why would I want to use the CGMS?" The answer is that occasional finger-stick blood tests do not provide an accurate picture of blood sugar values and excursions during the course of the day. MiniMed presented several graphical representations of the results from the CGMS sensor compared to finger stick blood tests. One graph looked something like this:
In this hypothetical graph, finger-stick blood glucose data, shown in red, appear to show excellent blood sugar control. The CGMS sensor, however, identified periods of severe hypoglycemia before waking and severe hyperglycemia after breakfast.
The personal computer software produces graphs similar to this, as well as numerical summaries of average glucose readings and other statistical data. The patient's physician will use these graphs and data to identify periods of the day when the patient should perform more finger-stick blood glucose tests. In this example, the patient would likely be asked to test around 2:00 am to identify night-time hypoglycemia, and at 10:00 am to identify post-meal hyperglycemia. Data from finger-stick blood tests would then be used to adjust the patient's diabetes management program. After implementing any recommended changes, the patient might be asked to wear the CGMS again after a month or two to validate that the changes are having the desired effect.
Real-Time Use of the Technology
Laboratory testing conducted by MiniMed in animals revealed that interstitial fluid lags high glucose levels in the blood by as much as 10 minutes. However, interstitial fluid shows lower glucose levels about 10 minutes before blood does. An alarm based on interstitial fluid could conceivably provide an early warning to impending hypoglycemia. Real-time use of the CGMS is a goal of MiniMed, but is not available in the product as approved by the FDA panel.
Even in its current, limited form, the CGMS offers patients with diabetes an unprecedented opportunity to see what their blood sugar values are throughout the day. This insight will help patients and physicians determine patterns of hypoglycemia and hyperglycemia that may have been undetected, allowing patients to make changes to their diabetes management program.
Posted 27 February 1999
Updated 13 October 2000
Last Updated: Thursday February 10, 2005 20:16:55
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