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 HbA1c at baseline. The 112 participants who were randomised to the closed-loop arm were divided into five HbA1c 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 HbA1c 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 HbA1c <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 HbA1c 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 HbA1c levels or because the user has already achieved their glycaemic targets, as both groups were able to benefit.