Carbohydrate-to-Insulin Ratio Is Estimated from 300-400 Divided by Total Daily Insulin Dose in Type 1 Diabetes Patients Who Use the Insulin Pump

Background: To optimize insulin dose using insulin pump, basal and bolus insulin doses are widely calculated from total daily insulin dose (TDD). It is recommended that total daily basal insulin dose (TBD) is 50% of TDD and that the carbohydrate-to-insulin ratio (CIR) equals 500 divided by TDD. We recently reported that basal insulin requirement is approximately 30% of TDD. We therefore investigated CIR after adjustment of the proper basal insulin rate. Subjects and Methods: Forty-five Japanese patients with type 1 diabetes were investigated during several weeks of hospitalization. The patients were served standard diabetes meals (25-30 kcal/kg of ideal body weight). Each meal omission was done to confirm basal insulin rate. Target blood glucose level was set at 100 and 150 mg/dL before and 2 h after each meal, respectively. After the basal insulin rate was fixed and target blood glucose levels were achieved, TBD, CIR, TDD, and their products were determined. Results: Mean (+/- SD) blood glucose levels before and 2 h after meals were 121 +/- 47 and 150 +/- 61 mg/dL, respectively. TDD was 31.5 +/- 9.0 U, and TBD was 27.0 +/- 6.5% of TDD. CIR x TDD of breakfast was significantly lower than those of lunch and supper (288 +/- 73 vs. 408 +/- 92 and 387 +/- 83, respectively; P < 0.01). Conclusions: CIR has diurnal variance and is estimated from the formula CIR = 300/TDD at breakfast or CIR = 400/TDD at lunch and supper in type 1 diabetes patients. These results indicate that the insulin dose has been underestimated by using previously established calculations.