https://diabetes.acponline.org/archives/2017/02/10/3.htm

Continuous glucose monitoring associated with lower HbA1c in type 1 diabetes treated with insulin injection

An editorial accompanying the two trials of continuous glucose monitoring stressed that the physicians involved had extensive experience with the technology and noted that the necessary changes in lifestyle and insulin dosing can be variable and complicated.


Continuous glucose monitoring (CGM) in patients with type 1 diabetes who inject insulin multiple times each day was associated with greater decreases in HbA1c versus usual care, two recent studies found.

In the first study, a randomized clinical trial at 24 U.S. endocrinology practices from October 2014 to December 2015, researchers examined whether CGM was effective in patients with type 1 diabetes who used daily insulin injections rather than an insulin pump. Included patients with HbA1c levels of 7.5% to 9.99% were randomly assigned in a two to one ratio to receive CGM or usual care. Patients assigned to CGM were provided with a CGM system and were asked to use it daily, calibrate it twice daily, and verify the glucose concentration with a blood glucose meter before injecting insulin. Patients assigned to the control group were asked to use home blood glucose monitoring at least four times per day. General education on diabetes management was provided to both groups. The study's primary outcome measure was difference in change in HbA1c level from baseline to 24 weeks, as measured by a central laboratory. Results were published in the Jan. 24/31 JAMA.

One hundred fifty-eight patients were included in the study, 105 who were assigned to CGM and 53 who were assigned to usual care. Mean patient age was 48 years, and 44% were women. Mean HbA1c level at baseline was 8.6%; median duration of diabetes was 19 years. One hundred fifty-five of 158 patients (98%) completed the study. At 12 weeks, mean reduction in HbA1c from baseline was 1.1% in the CGM group versus 0.5% in the usual care group; at 24 weeks, it was 1.0% versus 0.4%. The adjusted treatment group difference in mean change in HbA1c from baseline was −0.6% (P<0.001). Patients in the CGM group also spent a shorter time at a glucose level below 70 mg/dL (3.9 mmol/L), 43 min/d versus 80 min/d for the control group (P=0.002). Two patients in each group had a severe hypoglycemic event.

The researchers noted that their results may not apply to younger patients or to those whose HbA1c levels did not fall within the study range and that they should not be generalized to patients with type 2 diabetes, among other limitations. However, they concluded that in adults with type 1 diabetes who use multiple injections of insulin daily, CGM resulted in greater decreases in HbA1c over 24 weeks. They called for future studies to assess effectiveness over the longer term, clinical outcomes, and adverse effects.

The second study, an open-label crossover randomized clinical trial, was conducted from February 2014 to June 2016 and was published in the same issue of JAMA. Patients with type 1 diabetes at 15 outpatient diabetes clinics in Sweden who injected insulin multiple times daily and had an HbA1c level of 7.5% or greater were assigned to receive CGM treatment or conventional treatment for 26 weeks, with a 17-week washout period in between. Outcome measures were difference in HbA1c between weeks 26 and 69 and adverse events (e.g., severe hypoglycemia).

A total of 161 patients were included in the study, 142 of whom had follow-up data for both of the treatment periods. The mean patient age was 43.7 years, and 45.3% were women. Mean HbA1c among all patients was 8.6%; during CGM use, mean HbA1c was 7.92% compared with 8.35% during conventional treatment (mean difference, −0.43%; P<0.001). Severe hypoglycemia was noted in five patients in the conventional treatment group and one patient in the CGM group. In addition, seven patients had severe hypoglycemia during the washout period when conventional therapy was used.

The authors noted that about 12% of patients had no follow-up data in the second treatment period and that the study could not be blinded. However, like the authors of the first study, they concluded that CGM resulted in a lower HbA1c over the length of their study and called for further research on outcomes and long-term effects.

An accompanying editorial also pointed out several limitations about the findings of both studies and their generalizability, including concerns about costs and the potential differences between patients motivated to participate in clinical trials and typical patients. The editorialist stressed that the physicians involved in these two studies had extensive experience with CGM and noted that the necessary changes in lifestyle and insulin dosing in response to CGM data can be variable and complicated. “This will preclude most nonendocrinologists from using CGM (real-time or masked) in light of their time constraints in managing care for many patients with diabetes,” the editorialist wrote. He agreed with the authors of both trials that more studies of this treatment method are needed.