Continuous glucose monitoring (CGM) has been demonstrated in randomized trials to improve glucose control in patients with type 1 diabetes (T1D) (1–3); however, most of the participants in these trials have used a pump for insulin delivery, and the use of CGM in T1D patients receiving insulin by injection has not been well studied.
We used the T1D Exchange registry database to assess the impact of CGM on HbA1c in insulin injection users. Details on the informed consent process, eligibility criteria, and data collection methods have been previously published (4). Participants were defined as CGM users if CGM was used for real-time diabetes management during the 30 days prior to the clinic visit.
Among the 17,731 registry participants with T1D duration >1 year who had a clinic visit between June 2014 and October 2015, 6,222 (35%) used injections alone, 8,783 (50%) used pump alone, 2,316 (13%) used pump with CGM, and 410 (2%) used injections with CGM. A Dexcom CGM was being used by 97% of the injection + CGM users and by 58% of the pump + CGM users. Of the 2,726 participants using CGM, 85% were receiving pump treatment, and only 15% were receiving injections. The median number of boluses of short-acting insulin per day was 3 (interquartile range 3, 4) in both participants using injections alone and participants using injections with CGM. Participant and clinical characteristics by insulin method and CGM use are available at http://email.t1dxresearch.org/mdicgi/Supplemental%20Table%20S1.pdf.
Among CGM users, mean HbA1c was similar in injection and pump users (7.6 ± 1.3% vs. 7.7 ± 1.1%, P value from a linear mixed model adjusted for age, diabetes duration, race/ethnicity, education level, insurance status, annual income, and blood glucose meter testing frequency = 0.82) and lower in CGM users than in non-CGM users in the pump group (8.3 ± 1.5%, adjusted P < 0.001) and in the injection group (8.8 ± 1.9%, adjusted P < 0.001). As shown in Fig. 1, this pattern was seen in both adults and youth.
Mean HbA1c according to insulin modality/CGM use status. Solid black bar, injection + CGM; solid white bar, pump + CGM; black and white striped bar, pump only; black dotted bar, injection only.
Mean HbA1c according to insulin modality/CGM use status. Solid black bar, injection + CGM; solid white bar, pump + CGM; black and white striped bar, pump only; black dotted bar, injection only.
In this analysis of T1D Exchange registry data, CGM users, irrespective of insulin delivery method, had lower HbA1c levels than non-CGM users even after adjustment for potential confounding factors. Importantly, CGM users who were using injection for insulin delivery had HbA1c levels similar to those of CGM users using an insulin pump. This is consistent with the results from the JDRF CGM randomized controlled trial in which 9 adult injection/CGM users had a magnitude of HbA1c improvement similar to that of 41 adult pump/CGM users (−0.54 vs. −0.50) (2).
Although the results of this study appear to make a compelling case for greater use of CGM in injection users, cross-sectional analyses such as this one are subject to potential bias. For instance, we do not have information on how many injection users tried CGM and discontinued it, and thus, the cohort of injection + CGM users in the study may be self-selected to be those who are more likely to have lower HbA1c levels. Nevertheless, the results of the study suggest that CGM can be beneficial for insulin injection users across all age-groups to achieve optimized metabolic control of T1D. However, the critical information needed to assess the benefit of CGM for injection users will require a randomized trial focusing on injection users.
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Funding and Duality of Interest. Funding was provided by The Leona M. and Harry B. Helmsley Charitable Trust. W.V.T. has received consultancy payments from Novo Nordisk. R.M.B.’s nonprofit employer has received consultancy payments from Abbott Diabetes Care, Amylin Pharmaceuticals, Bayer, Boehringer Ingelheim, Calibra Medical, Eli Lilly, Halozyme Therapeutics, The Leona M. and Harry B. Helmsley Charitable Trust, Hygieia, Johnson & Johnson, Medtronic, Novo Nordisk, ResMed, Roche, Sanofi, Takeda, and Valeritas and grants from Abbott Diabetes Care, Amylin, Bayer, Becton Dickinson, Boehringer Ingelheim, Calibra, Daiichi-Sankyo, Dexcom, Eli Lilly, Halozyme Therapeutics, The Leona M. and Harry B. Helmsley Charitable Trust, Hygieia, Intarcia Therapeutics, Intuity Medical, Johnson & Johnson, MannKind Corporation, Medtronic, Merck, National Institutes of Health, Novo Nordisk, ResMed, Roche, Sanofi, and Takeda with no personal compensation to R.M.B. R.M.B. receives royalties from the Betty Crocker Diabetes Cookbook and holds stock in Merck. R.W.B.’s nonprofit employer has received consultancy payments on his behalf from Sanofi and Animas Corporation and a research grant from Novo Nordisk with no personal compensation to R.W.B. No other potential conflicts of interest relevant to this article were reported.
Author Contributions. N.C.F. and K.M.M. researched data, performed statistical analyses, and wrote and edited the manuscript. W.V.T., R.M.B., and R.W.B. researched data and reviewed and edited the manuscript. R.W.B. is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
