Analysis of guidelines for basal-bolus insulin dosing: basal insulin, correction factor, and carbohydrate-to-insulin ratio.

Objective: To analyze and compare the underlying mathematical models for basal-bolus insulin-dosing guidelines in patients with type 1 diabetes in a retrospective controlled study.

Methods: Algebraic model-development yielded several systems of models with unknown constants, including 3 systems currently in use. These systems were compared for logic and consistency. One of these systems was the accurate insulin management (AIM) system, which we developed in the setting of our large endocrine practice. Our database consisted of retrospective clinical records for a 7-month period. During this time, correction factor (CF), carbohydrate-to-insulin ratio (CIR), and basal insulin were being adjusted incrementally by titration. The variables studied were height, body weight in pounds (BWlb), CF, CIR, hemoglobin A1c (A1C), basal insulin, and 6-day mean total daily dose of insulin (TDD). The values of the variables used in the study were those determined on arrival of the patients at the office. The last 6 TDDs were entered into the database, and the mean was calculated by formulas within the database. We sorted our database into 2 groups, a well-controlled test group (n = 167; A1C 180 days, no severe hypoglycemic events since the last office visit, and C-peptide level 7% or time on pump <180 days). We obtained one office visit per patient, as follows: from the test group, we chose the visit with the lowest A1C value; from the control group, we chose one visit by use of a computer's random number generator. A significant difference was demonstrated between the correlation constants of the test group versus the control group by performing T tests between the means and F tests between the standard deviations. The least squares estimates of the correlation constants from the test group were recommended in the guidelines, in place of the means, to gain accuracy. By these methods, the guidelines used by the patients with good glycemic control are made available for all patients.

Results: With use of the AIM system, the TDD for continuous subcutaneous insulin infusion = 0.24 * BWlb; basal insulin = 0.47 * TDD; CF = 1,700/TDD; and CIR = 2.8 * BWlb/TDD.

Conclusion: Three mathematical models for CIR are presented, with a rationale for supporting one of them (the AIM model). This model, together with 3 related AIM models, when provided with statistically correlated constants, constitutes the AIM system of guidelines, a consistent and convenient means of estimating insulin-dosing variables for patients with type 1 diabetes.