Overnight Dosing Success in T1D Children

Hybrid Closed-Loop achieves glucose targets with less insulin; Good news for parents

Ulrike Schierloh, MD is with the Pediatric Clinic, Centre Hospitalier de Luxembourg, Luxembourg

We spoke with Ulrike Schierloh, MD who is with the Pediatric Clinic, Centre Hospitalier de Luxembourg, Luxembourg, GD de Luxembourg about the study that was just published in PLOS|One.

Study Overview

This study obtained glucose levels as well as plasma insulin levels in children with type 1 diabetes to evaluate the efficacy of a model—based closed-loop algorithm compared to an open-loop administration.  The model predicted control algorithm used by the group came from Prof. Hovorka and his team at Cambridge Univerity. This is a different algorithm to the one used in the Medtronic 670G but the principle of the hybrid closed loop is the same in the study as with auto-mode of the 670G.


Fifteen children with type 1 diabetes, 6–12 years, participated in this open-label single center study. We used a randomized cross over design in which we compared overnight closed-loop insulin delivery with sensor-augmented pump therapy for two nights in both the hospital and at home (i.e., 1-night in-patient stay and at home per treatment condition). During the in-patient stay, hourly plasma insulin and blood glucose levels were assessed.


Results of paired sample t-tests revealed that although plasma insulin levels were significantly lower during the closed-loop than in the open-loop (Mean difference 36.51 pmol/l; t(13) = 2.13, p = .03, effect size d = 0.57), blood glucose levels did not vary between conditions (mean difference 0.76 mmol/l; t(13) = 1.24, p = .12, d = 0.37). The administered dose of insulin was significantly lower during the closed-loop compared with the open-loop (mean difference 0.10 UI; t(12) = 2.45, p = .02, d = 0.68).


Lower insulin doses were delivered in the closed-loop, resulting in lower plasma insulin levels, whereby glucose levels were not affected negatively. This suggests that the closed-loop administration is better targeted and hence could be more effective.

Implications for Parents

Comments by Ulrike Schierloh, MD

A closed-loop system results in less hypoglycemia, and well-controlled children get more sleep, as do their parents.  Many parents tell us they are less afraid once they develop confidence in the system. This results in their kids having more independence.

The Medtronic 670G is the only currently available hybrid closed-loop system.  

This system is not as automatic as parents would like because security system requirements are high.  For example, the system will ask after a certain time that you confirm the minimum dose or maximum dose given by the automatic system of the 670G.  This can be particularly annoying with high BG variability such as with exercise. Also, the system target is fixed at a BG target of 120 which is higher than some people prefer.

These somewhat frustrating security requirements result in the pump switching from auto-mode to manual mode when the user does not provide the extra-glucose values requested by the pump.

It is logical that the first closed loop systems would have conservative security requirements but parents and users hope that less onerous requirements and better ease of use will come in the future.


Martin is the Founder of SelfRx Media and editor-in-chief of Insulin Nation. He's a passionate about sharing knowledge with those affected by Diabetes.

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