The Effect of Continuous Glucose Monitoring in Well-Controlled Type 1 Diabetes

OBJECTIVE

The potential benefits of continuous glucose monitoring (CGM) in the management of adults and children with well-controlled type 1 diabetes have not been examined.

RESEARCH DESIGN AND METHODS

A total of 129 adults and children with intensively treated type 1 diabetes (age range 8–69 years) and A1C <7.0% were randomly assigned to either continuous or standard glucose monitoring for 26 weeks. The main study outcomes were time with glucose level ≤70 mg/dl, A1C level, and severe hypoglycemic events.

RESULTS

At 26 weeks, biochemical hypoglycemia (≤70 mg/dl) was less frequent in the CGM group than in the control group (median 54 vs. 91 min/day), but the difference was not statistically significant (P = 0.16). Median time with a glucose level ≤60 mg/dl was 18 versus 35 min/day, respectively (P = 0.05). Time out of range (≤70 or >180 mg/dl) was significantly lower in the CGM group than in the control group (377 vs. 491 min/day, P = 0.003). There was a significant treatment group difference favoring the CGM group in mean A1C at 26 weeks adjusted for baseline (P < 0.001). One or more severe hypoglycemic events occurred in 10 and 11% of the two groups, respectively (P = 1.0). Four outcome measures combining A1C and hypoglycemia data favored the CGM group in comparison with the control group (P < 0.001, 0.007, 0.005, and 0.003).

CONCLUSIONS

Most outcomes, including those combining A1C and hypoglycemia, favored the CGM group. The weight of evidence suggests that CGM is beneficial for individuals with type 1 diabetes who have already achieved excellent control with A1C <7.0%.Over the past 15 years, the use of rapid and long-acting insulin analogs, improvements in insulin pumps, and more frequent home blood glucose monitoring have had a positive impact on the ability to achieve target A1C levels in type 1 diabetes. However, the rates of severe hypoglycemia remain too high and the occurrence of such events is often followed by a decline in glycemic control due to fears of further hypoglycemic episodes (1). Hypoglycemia remains the major limiting factor for achieving euglycemia in type 1 diabetes (2).The introduction of new real-time continuous glucose monitoring (CGM) systems has generated great interest because these devices may have the potential to increase the proportion of patients who are able to maintain target A1C values while simultaneously limiting the risk of severe hypoglycemia. In a randomized trial of 322 adults and children with type 1 diabetes and baseline A1C level ≥7.0%, our Juvenile Diabetes Research Foundation (JDRF) Continuous Glucose Monitoring Study Group reported that CGM substantially improved A1C levels without increasing the frequency of hypoglycemia in adults ≥25 years of age, whereas the lowering of A1C levels in children and adolescents was more limited (3). As with virtually every other study of a new drug or device in the treatment of type 1 diabetes, this study excluded individuals already reaching target A1C levels <7.0% because lowering of A1C was the primary outcome of interest. Consequently, our study group also conducted a separate, concurrent randomized trial to evaluate the efficacy and safety of CGM in adults and children with type 1 diabetes who already had successfully achieved A1C levels <7.0% with intensive insulin therapy.