Objective: Formulas to determine Insulin-Carbohydrate Ratio (ICR) use total daily dose (TDD) such as the 450 Rule (450/TDD=ICR) or body weight (BW) (2.8*weight in pounds/TDD). These do not account for age differences or adjust for HCL therapy.
Methods: We analyzed data from Medtronic 670G users meeting the following criteria: Time in Range (TIR, 70-180mg/dl) >65%, Time <70mg/dl <5%, A1c <8%, HCL for >3 months. Subjects were grouped by age: pre-pubertal, pubertal, and adult (18+). Subjects’ current ICR was multiplied by TDD at each meal to determine a formula starting point.
Results: 50 subjects were included (age 6-62, mean A1c 7.2%, TDD 0.8 u/kg/day, TIR 75%, 2.5% <70mg/dl). Compared to baseline, ICRs in HCL were made 10-26% more aggressive. ICRs calculated from the 450 rule were 15-41% less aggressive compared to the ratios used by HCL subjects. BW formula ICRs were too aggressive for pre-pubertal, closely matched the pubertal subjects, and underestimated meal bolus needs in adults on HCL.
Conclusions: Our data offers new initial ICR formulas for HCL users instead of the 450/TDD rule, i.e., a 300/TDD for adults and a 350/TDD for pubertal and prepubertal children at lunch/dinner, and a breakfast 300/TDD rule. Fine-tuning is necessary for each patient, but this offers a better tuned starting point for subjects starting HCL, helping minimize HCL exits due to post-prandial hyperglycemia.
I. Tabatabai: None. B.A. Buckingham: Advisory Panel; Self; ConvaTec Inc., Novo Nordisk Inc., Profusa, Inc. Consultant; Self; Medtronic MiniMed, Inc. Research Support; Self; Beta Bionics, ConvaTec Inc., Dexcom, Inc., Insulet Corporation, Medtronic MiniMed, Inc., Tandem Diabetes Care. Other Relationship; Self; Insulet Corporation, Tandem Diabetes Care.