Diabetes and Continuous Glucose Monitoring (CGM)
Technology continues to be a significant adjunct in the management of chronic illness, even more so in people with diabetes. A recent article by Konoff et. al. "Continuous Glucose Monitoring: An Endocrine Society Clinical Practice Guideline," published in The Journal of Clinical Endocrinology and Metabolism summarized the benefits of CGM in adults, children, and adolescents. The purpose of the paper was to "formulate practice guidelines for determining settings where patients are most likely to benefit from the use of continuous glucose monitoring." A task force was developed to include diabetes experts, a methodologist, and a medical writer. "An evidence-based guideline was developed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) system to describe both the strength of recommendations and the quality of evidence."
The task force evaluated three potential applications of continuous glucose monitoring relying on evidence-based literature in which there was enough data to recommend the use of CGM:
1. Real-time outpatient CGM in children at least 8 years of age and adolescents
2. Real-time outpatient CGM in adults
3. Real-time inpatient CGM in adults
The guidelines also suggested intermittent "diagnostic" application of CGM in both children and adults to analyze blood glucose patterns overnight (low blood sugars, dawn phenomena) and post-meal hyperglycemia. The data did not support the use of CGM in the intensive care unit or operating room until there is a further supporting documentation.
Based on the above recommendations, several questions must be asked:
1. Should all children (older than 8 years of age), adolescents, and adults with diabetes begin continuous glucose monitoring?
2. Should insurance carriers assume the cost of this equipment?
3. Should users of CGM wear the monitor all the time, intermittently, once a week, once a month, etc.?
4. Are CGM's necessary to enable successful management of diabetes?
Let's review how CGM really works. The CGM requires a sensor to be placed subcutaneously that measures the glucose in interstitial fluid (not blood) continuously but lags approximately 20-30 minutes behind serum glucose levels. The CMG graphically demonstrates interstitial glucose trends with arrows revealing upward, stable, and downward fluctuations of blood sugars. The CGM is not meant to replace self blood glucose monitoring, rather the purpose is to alert the user to check blood sugars more appropriately at times where the system is noting significant fluctuations upward or downward. SBGM is always recommended prior to eating in order to correctly calculate a correction bolus in addition to the food bolus. In summary, the CGM, at present, measures interstitial glucose trends as a proxy for blood glucose, but does not communicate with an insulin pump providing appropriate directions for insulin administration. YET. Research is actively underway to provide a closed feedback loop to marry the CGM with the insulin pump. Prototypes are in progress using different algorithms to make the unification of blood glucose and insulin therapy a reality (artificial pancreas).
As with all equipment that assists in the management of an illness, the device must be used appropriately. Clearly if the CGM is not worn, data will not be available. Herein lies the crux of the matter: for the CGM to be effective, it must be worn and data acted upon. If the CGM is in the closet most of the time, it is not worth the expense and bother. If the device is not utilized, the time associated with CGM training and utilization is not cost-effective.
At this juncture, CGM is not yet considered "standard of care." However, once research and technology solve the union of the insulin pump and CGM, the "artificial pancreas" certainly will become the state-of-the-art management of diabetes. We are at another crossroads in diabetes technology and are working to determine for which group or subgroup the CGM is most beneficial.
As I do not have definitive answers to questions 1-4, the best response is to discuss how our diabetes team at Children's National Medical Center utilizes the CGM. We do not have specific age group guidelines. If a child/adolescent or caregiver inquires about the CGM, we provide information as to how it works and the information it provides. We often perform CGM "diagnostics" in which the person with diabetes is blinded to the results that are then downloaded and analyzed by the team to determine trends and patterns. If the child is comfortable wearing the monitor and the family understands that the CGM does not take the place of SBGM, we will help the family obtain a personal CGM.
Intensive education is provided to use the CGM successfully and appropriately. We recommend that the CGM be used continuously for the best results or at least one week a month to evaluate trends. Unfortunately, many families abandon the CGM once they realize that a great deal of effort is required to set up, use, and interpret the information. However, there is a subgroup of children and motivated adolescents that do enjoy and use the CGM system productively. Our team will recommend CGM for children and adolescents that have significant fluctuations of blood sugars (and severe hypoglycemia) in an effort to better manage diabetes safely. In these situations, letters of medical necessity for insurance companies are appropriate.
In summary, CGM can be of major assistance in the evaluation of blood sugar trends and thus serve as an additional prompt or safety net to take action before the development of an unfavorable event and deliver insulin safely.