Diabetes Dialogue: Building A Consensus Definition for Fully Closed-Loop Systems

Welcome back to Diabetes Dialogue: Technology, Therapeutics, & Real-World Perspectives!

Automated insulin delivery (AID) systems still rely on meal and exercise announcements, and a new consensus framework sets the bar fully closed-loop (FCL) systems must clear in type 1 diabetes.

In this episode of Diabetes Dialogue, hosts Diana Isaacs, PharmD, and Natalie Bellini, DNP, spoke with Brynn Marks, MD, MSHPEd, of Breakthrough T1D, first author of the new roadmap.

The framework updates a Breakthrough T1D, formerly known as JDRF, roadmap first issued in 2009 and revised in 2015.1,2 Rather than prescribing a technology, it holds systems built on artificial intelligence, multi-hormone delivery, multi-analyte sensing, or adjunctive therapy to uniform outcome standards.1 Every FCL system must perform without mandatory meal or activity announcements.

Classification rests on time in tight range (TITR) of 70 to 140 mg/dL, time below 54 mg/dL under 1%, and validated person-reported outcomes.1 Class 3 systems must exceed 50% TITR, roughly equivalent to 70% time in range, while Class 2 and Class 1 systems must exceed 70% and 90%, respectively.1 Class 1a adds a 30-minute standardized moderate exercise test with no time below 54 mg/dL.1

The authors chose TITR because emerging evidence ties it more closely than time in range to microvascular complications and glycemic variability. The exercise test starts with glucose in tight range and no carbohydrate intake in the prior 2 hours, limiting insulin on board.

Person-reported outcomes carry equal weight. Trials must enroll representative populations and show meaningful gains in diabetes distress and quality of life among participants with low baseline scores, without deterioration among those already doing well. The requirement guards against trials enrolling only highly engaged participants on low-carbohydrate diets.

Neural network systems now in phase 3 trials need no second hormone or adjunctive drug, though their speed of adapting to day-to-day activity shifts remains uncertain. Glucagon-like peptide-1 (GLP-1) receptor agonists blunt postprandial excursions but carry gastrointestinal adverse effects. Dual glucose-ketone sensing may also renew interest in sodium-glucose cotransporter 2 (SGLT2) inhibitors as adjuncts.

Education needs will shift rather than disappear. Clinicians will still match people to systems, teach recognition of infusion site failure, and support transitions such as the move from pediatric to adult care. Less visit time spent on glucose may free room for lipids, blood pressure, and other complication risks.

Collectively, the framework gives developers, researchers, and clinicians a shared benchmark for FCL performance. It positions reduced self-management burden alongside near-normoglycemia as the defining goals of next-generation AID.

Editors’ Note: Isaacs reports disclosures with Dexcom, Abbott, Lilly, Novo Nordisk, Medtronic, Insulet, and others. Bellini reports disclosures with Abbott Diabetes Care, MannKind, Povention Bio, and others.

References

1. Marks BE, Hilliard ME, Kovatchev B, et al. Roadmap to fully closing the loop to optimize health in type 1 diabetes. Diabetes Technol Ther. Published online October 9, 2026. doi:10.1177/15209156261496643

2. Kowalski A. Pathway to artificial pancreas systems revisited: moving downstream. Diabetes Care. 2015;38(6):1036-1043. doi:10.2337/dc15-0364