Using set basal rates for [ldquo]sick day rules[rdquo] in hybrid closed-loop therapy could result in insufficient insulin delivery

Lili Bidari; Allison Low

doi:10.1530/endoabs.111.P23

P23

Prev Next

Section Contents Cite

Endocrine Abstracts (2025) 111 P23 | DOI: 10.1530/endoabs.111.P23

BSPED2025 Poster Presentations Diabetes 1 (9 abstracts)

Using set basal rates for “sick day rules” in hybrid closed-loop therapy could result in insufficient insulin delivery

Lili Bidari ^1,2 & Allison Low ¹

Author affiliations

¹Barnsley Hospital NHS Foundation Trust, Barnsley, United Kingdom; ²Sheffield Children’s NHS Foundation Trust, Sheffield, United Kingdom

Background: In acute illness, hybrid closed-loop (HCL) therapy may not cope with illness-associated hyperglycaemia. Temporary increased basal rates in manual mode (+30% and +50%) can be utilised. However, most pumps deliver basal insulin independently of the set basal rate and may automatically deliver significantly more than the set rate. Reverting to manual mode may lead to lower insulin delivery, even with temporary increased basal rates.

Aims: To review how quickly automated (delivered) basal rates increase in paediatric patients receiving HCL therapy and to predict how outdated set basal rates could affect insulin delivery when using sick day rules.

Methods: Review of clinic documentation and insulin pump data was conducted on a 3-monthly basis up to 12 months for paediatric patients with T1DM receiving HCL therapy in April 2024 at Barnsley Hospital. Data collection was completed at the end of August 2025; 100% of patients had concluded data collection.

Results: 86 patients were included; 67% used an Omnipod 5, MiniMed 780G, or CamAPS system. In this group, automated rates increased by an average of 4.6 units over 12 months. In our clinic, set basal rates increased by 4.1 units over the same period. If set basal rates were not updated, by 12 months patients would receive on average only 70% of their usual basal insulin if moved to manual mode. In manual mode with +30% and +50% temporary basal rates, 55% and 45% of patients respectively would receive less insulin than automated mode would have delivered. Sub-analysis by age and HCL system was also undertaken. Automated basal rates increased by 5.1 units on the t:slim X2 pump and set basal rates by 2.4 units. This pump uses set basal rates for automated insulin delivery so was excluded from the temporary basal rate analysis.

Discussion: Patients who use temporarily increased manual basal rates for sickness risk receiving less insulin than they would have in automated mode. There is a clinical risk of diabetic ketoacidosis if teams use this strategy without robust mechanisms to update basal rates. Sick day rules guidance should account for the clinical risk of outdated set basal rates.