Continuous Glucose Monitoring Systems
The difficulty in controlling blood glucose has been the variability over time. Most individuals with diabetes perform home glucose monitoring between 1-3 times per day. Even those who perform home glucose monitoring 5-7 or more times per day do not generally delineate the variability in glucose. Continuous glucose monitoring was developed in an attempt to resolve this dilemma and provide additional glucose control.
Several factors have been implicated in the limitations to achieving optimal glucose control. These include hypoglycemia, post-prandial hyperglycemia and glucose variability. These can be unpredictable and need to be recognized and addressed appropriately.
History and Early Use
The initial attempt at CGM was by Updike and Hicks. In 1967, the performed studies utilizing animal models.
The first device for human use was approved by the FDA in 1999. The GlucoWatch biographer was for retrospective view of glucose levels.
Unfortunately, the accuracy and other multiple issues with the device precluded widespread use. Irritation at the skin site was frequent. The accuracy and need to calibrate constantly were other issues. The device was sold to Animas corporation in 2005. Attempts to improve the device were not successful and the it was discontinued in 2007.
Devices available at Present
In the United States there are several devices available at present for personal use. DexCom has its new G4 Platinum, Medtronic has both the Guardian and combination insulin pump - CGM - Paradigm system. Abbott has the FreeStyle Navigator, though this is utilized mostly in Europe and Middle East.
Professional CGM is available via Medtronics iPro 2 system and DexCom which can be blinded for professional use.
Presently, CGM devices are approved as adjunctive to standard glucose testing via meters. Accuracy, though improving is still not considered equivalent to that of present glucose meter technology. There is also a physiologic lag between blood glucose measurements and that of interstitial space glucose. This is generally 5-10 minutes depending on the rapidity of glucose change. Thus, the possibility still exists for insulin stacking in the face of hyperglycemia and over treatment of hypoglycemia. Calibration of sensors is imperative and should be done when the glucose levels are stable.
Recent studies have indicated the improvement in Hemoglobin A1C levels were dependent on the frequency of CGM use. In 3 studies recently reported, there was an average - 0.76% decrease in A1C levels in those patients that used CGM over 1 year compared to non-users. Barriers to increase use of CGM include frequency of alarms, discomfort with sensor, cost and concerns with inaccuracy compared with standard home monitoring.
Over the past several years, there has been significant improvement in accuracy and reliability in CGM devices. In addition, the sensor itself has less discomfort. With continued improvement, it is anticipated that CGM use will increase and may prove more effective than standard home glucose monitoring.
^ Sharif A, McAuley SA, Horsburgh JC, Loh M, Jenkins AJ, MacIsaac RJ and O'Neal DN; The Role of Real Time Continuous Glucose Monitoring in People with Diabetes Managed with Multiple Daily Injections: Need for Future Research Infusystems USA 11(3) 17 2014
^ Updike SJ and Hicks GP: The enzyme electrode Nature; 214: 986 1967
^ Garg SK; The future of continuous glucose monitoring.
^ Garg SK, Voelmle M and Gottlieb PA; Tame lag characterization of two continuous glucose monitoring systems. Diabetes Research and Clinical Practice 87: 348 2010
^ Ellis SL, Naik RG, Gemperline K and Garg SK; Use of continuous glucose monitoring in patients with Type 1 diabetes. Current Diabetes Reviews 4: 207 2008
^ Anderson j, Attvall S, Sternemalm L, Pivodic A, Fahlen M, Hanas R, Ekeroth G and Lind M; Effect on Glycemic Control by Short and Long-Term Use of Continuous Glucose Monitoring in Clinical Practice.
^ McQueen RB, Ellis SL, Maahs DM, Anderson HD Nair KV and Campbell JD; Frequency of Continuous Glucose Monitoring Use and Change in Hemoglobin A1C for Adults with Type 1 Diabetes in a Clinical Practice Setting. Endocrine Practice 20: 1007 2014