Association of HbA1c to BOLUS Scores Among Youths with Type 1 Diabetes

Background: Frequency of mealtime insulin bolusing (BOLUS) is a promising new objective assessment of adherence in youths with type 1 diabetes (T1D). As further confirmation of the validity of BOLUS, we compare the associations of glycated hemoglobin (HbA1c) values of T1D youths with the original scoring of BOLUS and two alternative scoring procedures: mean mealtime boluses within a 2-h meal window (2h-BOLUS) and total daily frequency of boluses (TOTAL-BOLUS). In addition, we assess HbA1c associations of these three procedures, including interaction terms for mealtime boluses plus correction boluses. Subjects and Methods: Blood glucose meter data, insulin pump records, and HbA1c levels were collected from a combined clinical and research database for a random sample of 100 youths (mean age, 12.7 +/- 4.6 years). Youths' pump records were scored using the published methodology and alternative procedures for evaluating insulin use. Results: Youths' BOLUS, TOTAL-BOLUS, and mealtime boluses within a 2-h meal window (2h-BOLUS) scores are independently associated with youths' HbA1c level; all measures demonstrated stronger associations with youths' HbA1c than did frequency of glucose monitoring. The strongest association was between youths' BOLUS score and their HbA1c level. In multiple regression analyses, youths' BOLUS score better explains the variations in HbA1c levels than either youths' 2h-BOLUS or TOTAL-BOLUS scores. When combined with BOLUS in the same relationships, 2h-BOLUS and TOTAL-BOLUS were not found to have statistically significant coefficients. None of the bivariate relationships of HbA1c and interaction terms of mealtime and correction boluses was significant. Conclusions: The original method for calculating BOLUS appears superior to alternative scoring methods in its association with youths' HbA1c levels.