Twenty-seven published randomized controlled trials (RCTs) assessing outcomes of continuous glucose monitoring (CGM), involving a total of 3,826 patients, have been published to date. Although the number of patients in each study has been small compared to drug trials, cumulative evidence indicates a benefit of CGM for patients treated with either continuous subcutaneous insulin infusion (CSII) or a multiple daily injection (MDI) insulin regimen. Additionally, some data suggest that CGM may benefit people with type 2 diabetes who do not use insulin therapy.

Overall, RCTs have shown improved glucose control in patients with higher initial A1Cs (often in the range of 7.8–8.8%) using CGM compared to self-monitoring of blood glucose (SMBG). People who wear their CGM device most consistently derive the most benefit. Time spent in the designated hypoglycemia range (usually <70 mg/dL) was reduced in some studies, particularly in those with patients selected for having a higher risk of hypoglycemia. These patients tended to have lower baseline A1Cs (in the range of 6.5–7.5%). Rates of severe hypoglycemia generally have not differed between CGM and non-CGM groups, and these rates have been low across all studies.

Studies fall into a few basic categories: adults with type 1 diabetes (8 trials, 698 patients), adults with type 2 diabetes (4 trials, 547 patients), children with type 1 diabetes (2 trials, 227 patients), adults plus children with type 1 diabetes (7 trials, 1,084 patients), adults with type 1 or type 2 diabetes (3 trials, 655 patients), and women during pregnancy with either type 1 diabetes or gestational diabetes mellitus (GDM) (3 trials, 585 patients). Table 1 lists general findings from all of these trials. It is important to note that some trials used A1C or time in range as the primary endpoint, whereas others used time in a hypoglycemic range as the primary outcome. Readers should also be aware that Table 1 is not a meta-analysis per se, but rather includes studies identified through a literature search of PubMed and Ovid MEDLINE, as well as all prior reviews and studies in their reference lists. Only RCT data are included; observational studies and extension phases of RCTs also have been performed but are not represented here.

The first trials, from the early 2000s, used intermittent CGM. Some used “professional” CGM, in which patients were blinded to the CGM data (see the article on p. 8 of this compendium), and others followed an intermittent use schedule. As time progressed, the trials reflected evolving use of CGM to the current day. That is, earlier studies began to suggest that CGM could improve outcomes, but lack of access to real-time data limited benefit. More recent studies of real-time CGM, in which around-the-clock data are available, have shown more benefit in terms of reduction in both A1C and time spent in a hypoglycemic range.

A major impediment to interpreting CGM studies is that no uniform standard has been employed for teaching people with diabetes how to use continuous data, and no standard follow-up is provided to ensure that dose adjustments are made. In some trials, written instructions were provided to patients regarding insulin dose adjustments, but in many others, targeted education was not provided beyond how to use the device. Additionally, rapid advances in technology are not well represented in the literature, although data from newer systems, such as the Dexcom G5 Mobile (Dexcom, San Diego, CA) and the FreeStyle Libre (Abbott, Alameda, CA), are becoming available.

The opinions expressed are those of the authors and do not necessarily reflect those of Abbott Diabetes Care or the American Diabetes Association. The content was developed by the authors and does not represent the policy or position of the American Diabetes Association, any of its boards or committees, or any of its journals or their editors or editorial boards.

Dualities of Interest

I.B.H. has served as a consultant to Abbott Diabetes Care, Adocia, Bigfoot, and Roche. His institution has received research grant support from Medtronic.

T.B. has served on advisory boards of Bayer Health Care, Boehringer Ingelheim, DreaMed Diabetes, Eli Lilly, Medtronic, Novo Nordisk, and Sanofi. His institution has received research grant support, with receipt of travel and accommodation expenses in some cases, from Abbott Diabetes Care, Diamyd, GluSense, Medtronic, Novo Nordisk, Sandoz, and Sanofi. He has received honoraria for participating on the speakers bureaus of Bayer Health Care, Eli Lilly, Medtronic, Novo Nordisk, Roche, and Sanofi. He owns stock in DreaMed Diabetes.

A.L.P. has served on advisory boards for Abbott Diabetes Care, Becton Dickinson, Bigfoot, Boehringer Ingelheim, Eli Lilly, Lexicon, Livongo, Medscape, Merck, Novo Nordisk, OptumHealth, Sanofi, and Science 37. She has received research grant support from Dexcom and Mannkind. She participates on a speakers bureau for Novo Nordisk.J.J.C. participates in speakers bureaus for Janssen, Merck, Novo Nordisk, and Sanofi.

G.A. has served as a consultant and on a steering committee for Dexcom and on an advisory board for Novo Nordisk, and her institution has received research grant support from AstraZeneca and Novo Nordisk.

R.M.B.’s institution has received payment for his services as a research investigator, consultant, or advisory board member for Abbott Diabetes Care, Becton Dickinson, Boehringer Ingelheim, Bristol-Myers Squibb/AstraZeneca, Dexcom, Eli Lilly, Hygieia, Johnson & Johnson, Medtronic, Merck, Novo Nordisk, Roche, Sanofi, and Takeda. R.M.B. has inherited Merck stock, volunteers for the American Diabetes Association and JDRF, and receives funding from the National Institutes of Health for diabetes technology research.

Acknowledgments

Writing support services for this compendium were provided by Carol Verderese of The Diabetes Education Group in Lakeville, CT. Editorial and project management services were provided by Debbie Kendall of Kendall Editorial in Richmond, VA.

Author Contributions

All authors researched and wrote their respective section(s). Lead author I.B.H. reviewed all content and is the guarantor of this work.

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Suggested citation:

Hirsch IB, Battelino T, Peters AL, Chamberlain JJ, Aleppo G, Bergenstal RM. Role of Continuous Glucose Monitoring in Diabetes Treatment. Arlington, Va., American Diabetes Association, 2018

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