- A large registry study in young people with type 1 diabetes found that hybrid closed-loop systems were linked to slightly better HbA1c and more time in the target glucose range than open-loop pump therapy.
- The rate of hypoglycaemic coma was lower with hybrid closed-loop systems, but the rate of diabetic ketoacidosis (DKA) was higher.
- The results reinforce that automated insulin delivery can improve glucose control, but ketone awareness and sick-day management remain critical.
Type 1 diabetes is an autoimmune condition where the body no longer produces insulin.
Because insulin is essential for moving glucose into cells, people with type 1 diabetes need lifelong insulin treatment.
Insulin pumps and glucose sensors have transformed day-to-day management.
However, many people still struggle to stay within glucose targets and avoid acute complications.
In open-loop pump therapy, insulin delivery is set and adjusted manually.
In hybrid closed-loop systems, a sensor and algorithm automatically adjust basal insulin, while users still bolus for meals.
The study examined whether hybrid closed-loop systems change the risk of severe low glucose and DKA compared with open-loop therapy.
Researchers used data from the Diabetes Prospective Follow-up Registry (DPV).
Nearly 14,000 participants aged 2 to 20 years were included.
All had lived with type 1 diabetes for more than a year.
In total, 7,088 used hybrid closed-loop therapy and 6,834 used open-loop therapy. The median follow-up time was 1.6 years.
The primary outcomes were severe hypoglycaemia and ketoacidosis.
Researchers also compared HbA1c, time in range, and glucose variability.
Hybrid closed-loop users had a lower rate of hypoglycaemic coma.
Rates were reported as 0.62 per 100 patient-years for hybrid closed-loop versus 0.91 for open-loop therapy.
HbA1c was slightly lower in the hybrid closed-loop group.
Average HbA1c was 7.34% compared with 7.50% in the open-loop group.
Time in range was higher with hybrid closed-loop systems.
Participants spent about 64% of the time between 3.9 and 10.0 mmol/L compared with about 52% in the open-loop group.
Glucose variability was also lower in the hybrid closed-loop group.
Lower variability generally means fewer large swings between highs and lows.
The rate of severe hypoglycaemia was not significantly different between groups.
That suggests the main hypoglycaemia benefit was in reducing the most extreme events, rather than all severe lows.
The main concern was DKA.
Hybrid closed-loop therapy was associated with a higher DKA rate, reported as 1.74 events per 100 patient-years versus 0.96 with open-loop therapy.
The risk appeared especially high among those with poorer overall glucose control.
In participants with HbA1c at or above 8.5%, DKA rates were reported as 5.25 per 100 patient-years in the hybrid closed-loop group versus 1.53 in the open-loop group.
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The authors emphasised that this does not mean hybrid closed-loop systems are unsafe by default.
It points to the importance of user education, troubleshooting, infusion set management, and clear sick-day rules.
They specifically highlighted close monitoring of ketones when illness or insulin delivery problems are suspected.
Early ketone testing in blood or urine can help detect rising DKA risk before it becomes an emergency.
For families and young people using hybrid closed-loop systems, the practical message is balanced.
Automated insulin delivery can improve day-to-day control, but it does not remove the need for vigilance when something goes wrong.
Study reference: The Lancet Diabetes and Endocrinology (published via ScienceDaily summary, 13 February 2025), DPV registry analysis led by Prof Beate Karges, comparing hybrid closed-loop versus open-loop systems in children and young people with type 1 diabetes.
