Effect of switching from intermittently scanned to real-time continuous glucose monitoring in adults with type 1 diabetes: 24-month results from the randomised ALERTT1 trial

Background Comparing Continuous With Flash Glucose Monitoring In Adults With Type 1 Diabetes (ALERTT1) examined whether switching from first-generation intermittently scanned continuous glucose monitoring (isCGM) without alerts to real-time continuous glucose monitoring (rtCGM) with alert functionality offers additional benefits to adults with type 1 diabetes. The extension of the randomised ALERTT1 trial assessed the effect of switching from isCGM to rtCGM up to 24 months.Methods In this 6-month, double-arm, parallel-group, non-masked, randomised, controlled trial, done across six hospitals in Belgium, 254 adults aged 18 years or older with type 1 diabetes previously using isCGM were randomly assigned (1:1) to rtCGM with alerts (intervention; n=127) or isCGM without alerts (control; n=127). Upon completion of the 6-month trial, the control group switched to rtCGM (is-rtCGM group), and the intervention group continued rtCGM (rt-rtCGM group). The extension focused on within-group changes in time in range (TIR; 3.9-10.0 mmol/L; primary outcome), HbA(1c), time in clinically significant hypoglycaemia (<3.0 mmol/L), and Hypoglycaemia Fear Survey worry (HFS-worry) score (all prespecified key secondary outcomes). Mean within-group change versus the start of rtCGM is reported, with a positive value referring to a lower value at start of rtCGM. This trial is registered at ClinicalTrials.gov (NCT03772600).Findings 119 participants were assigned to the is-rtCGM group of whom 112 (94%) completed the 24-month trial, and 123 participants were assigned to the rt-rtCGM group of whom 117 (95%) completed the 24-month trial. TIR increased from 51.8% (95% CI 49.1-54.5) at start of rtCGM (month 6) to 63.5% (60.7-66.3) at month 12 in the is-rtCGM group, and remained stable up to month 24 (change 11.7 percentage points [pp] [9.4-14.0; p<0.0001). In the rt-rtCGM group, TIR increased from 52.5% (95% CI 49.8-55.1) at start of rtCGM (month 0) to 63.0% (60.3-65.8) at month 12, also remaining stable up to month 24 (change 10.5 pp [8.2-12.8]; p<0.0001). HbA1c decreased from 7.4% (57 mmol/mol; month 6) to 6.9% (52 mmol/mol) at month 24 (change -0.54 pp [95% CI -0.64 to -0.44]; -5 mmol/mol [95% CI -6 to -4]; p<0.0001) in the is-rtCGM group, and from 7.4% (57 mmol/mol; month 0) to 7.0% (53 mmol/mol) at month 24 (change -0.43 pp [95% CI -0.53 to -0.33]; -4 mmol/mol [95% CI -5 to -3]; p<0.0001) in the rt-rtCGM group. The change in HFS-worry score was -2.67 (month 24 vs month 6; p=0.0008) in the is-rtCGM group and -5.17 points (month 24 vs month 0; p<0.0001) in the rt-rtCGM group. Time in clinically significant hypoglycaemia was unchanged in both groups after month 12. Severe hypoglycaemia decreased from 31.0 to 3.3 per 100 patient-years after switching to rtCGM.Interpretation Glycaemic control and hypoglycaemia worry improved significantly up to 24 months after switching from isCGM without alerts to rtCGM with alerts, supporting the use of rtCGM in the care of adults with type 1 diabetes.