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Am Fam Physician. 2021;103(11):697

Clinical Question

Do continuous glucose monitoring devices improve glucose control?

Bottom Line

Only patients using intensive insulin therapy who are unsure of when they are extremely hypoglycemic or hyperglycemic should use continuous glucose monitoring. In patients who have diabetes mellitus who are treated with intensive insulin regimens, continuous glucose monitoring modestly decreases A1C in short-term, unmasked studies. The effect goes away when pregnant women and children are excluded from the analysis. Patients with type 2 diabetes made up only 19% of the total number of patients and were not analyzed separately. This meta-analysis had many reasons for not combining the results of the 15 studies—differences in patient demographics, high risk of bias, and extreme heterogeneity of results across the studies. (Level of Evidence = 1a−)


The authors searched four databases, including a trial registry and the Cochrane Registry, to identify 15 randomized trials that enrolled a total of 2,461 patients and followed up for three to nine months. Only three of the included studies comprised patients with type 2 diabetes, all of whom were treated with multiple daily doses of insulin; they accounted for only 19% of the total number of patients. Two researchers decided on study eligibility and extracted the data independently. There was very high heterogeneity among the patient characteristics across the studies. Ages ranged from 11.4 to 67 years, patients had type 1 or type 2 diabetes, and pregnant women were enrolled. There was very high heterogeneity (I2 greater than 90%) for most outcomes. The risk of bias was high for all of the studies because patients and the outcome assessors were aware of whether patients had continuous glucose monitoring. On average (with great variability), A1C decreased by 0.17% (which may translate into approximately 0.5 percentage points) with continuous glucose monitoring, but this difference went away when children and pregnant women were excluded. Time in appropriate glucose range, which is the percentage of time spent between 70 mg per dL and 180 mg per dL [3.89 and 9.99 mmol per L]), increased an average of 70 minutes per day. Time spent with severe hypoglycemia (less than 54 mg per dL [3.0 mmol per L]) was shorter with continuous glucose monitoring, although heterogeneity was 91.7% and there was evidence of publication bias. Time spent with severe hyperglycemia (more than 250 mg per dL [13.88 mmol per L]) was shorter with continuous glucose monitoring, with moderate heterogeneity among the studies.

Study design: Meta-analysis (randomized controlled trials)

Funding source: Unknown/not stated

Setting: Outpatient (any)

Reference: Maiorino MI, Signoriello S, Maio A, et al. Effects of continuous glucose monitoring on metrics of glycemic control in diabetes: a systematic review with meta-analysis of randomized controlled trials. Diabetes Care. 2020;43(5):1146–1156.

Editor's Note: Dr. Shaughnessy is an assistant medical editor for AFP.

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