CHICAGO — Findings from a recent study suggest that the combined real-time continuous glucose monitor/insulin pump system reduces glycemic variability and improves glucose control in selected insulin pump users with type 1 diabetes, Dr. Irl B. Hirsch reported at the annual scientific sessions of the American Diabetes Association.
A significant finding of the 6-month study was that the benefits of real-time continuous glucose monitoring (RT-CGM) were realized only in patients who wore the sensor device consistently, said Dr. Hirsch, professor of medicine and medical director of the Diabetes Care Center at the University of Washington, Seattle.
In the study, 138 adolescents and adults with poorly controlled type 1 diabetes (defined as having a hemoglobin A1c of 7.5% or greater) despite 6 months or more of insulin pump therapy were randomized to either wear the combined pump/RT-CGM device (MiniMed Paradigm 722 System) and to perform self-monitoring of blood glucose (SMBG) four or more times a day, or to perform SMBG while wearing the MiniMed pump by itself. All insulin adjustments were based on SMBG values. Clinical staff contacted the patients on a weekly or biweekly basis throughout the study period. The study was funded by Medtronic, maker of the devices.
The group was 90% white, nearly two-thirds female, and had a mean diabetes duration of 18 years. There were 40 adolescents with a mean age of 14 years, and 98 adults with a mean age of 41 years. Mean hemoglobin A1c (HbA1c) levels did not differ between the two groups at baseline.
At 13 weeks, mean HbA1c levels had dropped significantly and to a nearly identical degree in both groups, from 8.4% to 7.8% in the controls and from 8.5% to 7.7% in the CGM group. There were no further significant drops in either group, and by week 26, both groups had a mean HbA1c of 7.8%. However, the proportion reaching the HbA1c target of less than 7% was significantly greater in the CGM patients, at 38%, compared with 19% of the controls. Similar results were seen when the adults were analyzed separately.
Among the adolescents, only the CGM group had a significant drop in HbA1c from baseline, from 8.8% to 8.0% at 26 weeks, with 35% reaching an HbA1c below 7%, compared with just 9% of controls, said Dr. Hirsch.
Differences in the amount of hypoglycemia—but not hyperglycemia—could help explain why the proportion dropping below 7.0% between the two groups was significantly different, whereas the overall HbA1c values were not. Although there were no differences in the time and amplitude of exposure (in mg/dL per minute) for hyperglycemia between the two groups, the controls spent significantly more time at glucose levels below 70 mg/dL than did the CGM group (0.8 vs. 0.3 mg/dL per minute), suggesting that they had more glucose variability.
Compliance strongly predicted the results among the CGM patients. With “compliance” defined as wearing the sensor 6 days a week (meaning it was possible to be more than 100% compliant) HbA1c levels patients with 100% or greater compliance dropped from 8.6% at baseline to 7.7% at 26 weeks. Those with 80%–100% compliance dropped similarly, from 8.4% to 7.7%, as did those with 60%–80% compliance, 8.2% to 7.5%. All of those reductions were significant. However, when compliance dropped below 60%, mean HbA1c actually rose slightly (but not significantly), from 9.5% to 9.6%. In the teens, only those with 80%–100% compliance had a significant drop in HbA1c, by 1 percentage point from baseline.
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