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.

Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. More information is available at http://www.diabetesjournals.org/content/license.