Hybrid closed-loop technology and glycaemic outcomes according to baseline HbA1c

The iDCL (International Diabetes Closed-Loop) trial evaluated the use of a hybrid closed-loop insulin delivery system, comprising a t:slim X2 insulin pump with Control-IQ technology (Tandem Diabetes Care) and a Dexcom G6 continuous glucose monitor. The system’s main distinguishing features are automated hypoglycaemia prevention by reducing basal insulin delivery; automated hyperglycaemia mitigation by increasing the basal rate and administering automated boluses; and gradual narrowing of glycaemic targets at night. Users are required to control their mealtime bolus doses. The iDCL trial previously showed that the closed-loop system resulted in significantly greater time in range compared with sensor-augmented pump therapy (Brown et al, 2019).

The aim of this subanalysis of the iDCL trial was to determine whether glycaemic outcomes differed according to HbA_1c at baseline. The 112 participants who were randomised to the closed-loop arm were divided into five HbA_1c categories, ranging from <6.5% to ≥8.5%. In the overall cohort, percentage time in range (TIR) increased from 60.7% to 71.4% with use of the closed-loop system. Those with the highest HbA_1c at baseline saw the greatest increase in TIR, at 22.5%, and this was largely due to a reduction in time in hyperglycaemia, by 21.9%. However, even those with HbA_1c <6.5% saw an increase in TIR of 7.1%, largely due to a reduction in hypoglycaemia of 4.4% (3.6% during the day and 6.8% overnight).

The main limitations of this study was that the original trial was not sufficiently powered to conduct statistical tests between the HbA_1c subgroups; therefore, the results presented here are only descriptive in nature. It is also limited by a lack of diversity in the trial participants: most were non-Hispanic white, and the majority had private health insurance and a household income over US$100,000.

Despite these concerns, the authors conclude that the results are a strong argument not to restrict access to closed-loop technology either because of high HbA_1c levels or because the user has already achieved their glycaemic targets, as both groups were able to benefit.

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