Variable CGM benefits in high-risk subgroups
medwireNews: Continuous glucose monitoring (CGM) is well accepted and reduces time in hypoglycemia among older individuals with type 1 diabetes, report researchers in JAMA.
But a companion study in adolescents and young adults showed only a small effect on glycemic control, although this may have been affected by declining use of the technology over the 6 months of the study.
The study of older adults involved 203 people who were randomly assigned to use CGM or continue with self-monitored blood glucose (SMBG) for 6 months. The median ages were 68 and 67 years in the two groups, respectively, and a corresponding 59% and 44% were female, with average glycated hemoglobin (HbA1c) levels of 7.6% (60 mmol/mol) and 7.5% (58 mmol/mol).
During the final 4 weeks of the study, 81% of the participants in the CGM group were wearing the device 7 days/week, and 89% were using it at least 5 days/week.
In a linked editorial, Shivani Agarwal (Albert Einstein College of Medicine, New York, USA) and Anne Cappola (University of Pennsylvania, Philadelphia, USA) say this “bodes well for acceptability of more advanced CGM technologies and future artificial pancreas systems in older adults, which could have profound effects on glycemic control.”
The primary outcome of this study was time spent in hypoglycemia (<70 mg/dL; 3.9 mmol/L) – chosen because of the high risk for hypoglycemia in this age group, and the dangers associated with it, explain lead investigator Richard Pratley (AdventHealth Translational Research Institute, Orlando, Florida, USA) and colleagues.
The median proportion of time in hypoglycemia declined between baseline and 6 months in the CGM group from 5.1% (73 min/day) to 2.7% (39 min/day), whereas it remained relatively stable, at a corresponding 4.7% (68 min/day) and 49% (70 min/day) in the SMBG group. This gave a significant 1.9% (27 min/day) difference between the two groups, favoring CGM use.
The treatment benefit was evident from within the first month of use, and hyperglycemia, time in range, and HbA1c were also all significantly improved with CGM use versus SMBG. Just one person in the CGM group had a severe hypoglycemia episode, compared with 10 such events in the SMBG group, five of which involved seizure or loss of consciousness.
The editorialists note that the positive effect of CGM on hypoglycemia in this population “has health care use, mortality, morbidity, and economic benefits.”
By contrast, in the study of adolescents and young adults, CGM delivered improvements in glycemic control that, although positive, were small, with the primary outcome measure of HbA1c reducing from 8.9% at baseline to 8.5% at week 26 (74 to 69 mmol/mol) in the CGM group versus 8.9% at both timepoints in the SMBG group.
Agarwal and Cappola attribute this small benefit partly to the much less consistent use of CGM in this younger age group. By the end of the study only 68% of the participants were using CGM at least 5 days/week on average, and 14% (including three individuals who dropped out) were not using it at all.
Although this “may have attenuated the magnitude of primary outcome effects, [it] also may reflect realistic CGM use in this population” say the editorialists.
“Nevertheless, this modest glycemic improvement is encouraging with even suboptimal use of CGM,” they add. “The studied population faces challenges in improving glycemic control by any means.”
This study, from Kellee Miller (Jaeb Center for Health Research, Tampa, Florida, USA) and team, included 74 participants in the CGM group and 79 in the SMBG group, aged an average of 17 and 18 years, respectively (range 14–24 years). The between-group difference in HbA1c, although statistically significant, was just 0.37%. Nevertheless, the CGM group had significant reductions in time spent in hyperglycemia and hypoglycemia, and a corresponding 6.9% increase in time in range.
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