Determinants of glycaemic control in type 1 diabetes during intensified therapy with multiple daily insulin injections or continuous subcutaneous insulin infusion: importance of blood glucose variability

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Abstract
Background and methods We investigated the factors that determine the best glycaemic control on multiple daily insulin (MDI) injections and continuous subcutaneous insulin infusion (CSII), and the hypothesis that blood glucose variability is a major determinant of control and that the resultant HbA1c on MDI correlates with the improvement achieved by CSII. We studied 30 type 1 diabetic subjects already receiving MDI. Renewed attempts to improve control on MDI were made for a median of five months, and then the subjects were switched to CSII. The variability of within-day and between-day blood glucose concentrations was calculated from blood glucose self-monitoring data. Results HbA1c during MDI varied from 5.7 to 11.7% (mean ± SD, 8.5 ± 1.4%). Within- and between-day blood glucose variability correlated with HbA1c on MDI (r = 0.59, p < 0.001; r = 0.48, p < 0.03). Within-day variability remained an independent predictor of HbA1c on MDI. Mean HbA1c improved with CSII (to 7.3 ± 0.9%, p < 0.001), but reduction in HbA1c was variable and was related to the HbA1c on MDI (r = 0.79, p < 0.001) and within-day variability (r = 0.56, p < 0.01). Similar results were observed for subjects treated only with glargine-based MDI. Conclusions The best glycaemic control achievable on MDI is related to blood glucose variability—those with the largest swings in blood glucose retaining the highest HbA1c. The improvement in control achieved by CSII is related to HbA1c and blood glucose variability on MDI. Pump therapy is most effective in those worst controlled on MDI. Copyright © 2006 John Wiley & Sons, Ltd.