Timing of insulin bolus in patients with type 1 diabetes: Effect on glucose control and variability using CGMS

The aim of this non-randomised, pilot study was to examine the effect of insulin bolus injection timing on overall daily glucose control and glucose variability using a continuous glucose monitoring system (CGMS). Twelve patients with type 1 diabetes treated with either multiple daily insulin injections (MDI) or continuous subcutaneous insulin infusion (CSII), with HbA1c ≤7.5% (58mmol/mol), were connected twice to a CGMS for 72 hours. During period one the patients injected the insulin bolus before the meal and, during period two, after the meal. The variability of blood glucose (BG) was assessed by low BG indices (LBGI) and high BG indices (HBGI). the measure of the variability of low and high BG readings. Their sum (LBGI + HBGI) gives the BG risk index (BGRI). a measure of overall variability and deviations towards hypo- and hyperglycaemia. Six patients were on CSII and six on MDI. The number of meals, number of insulin injections and average BG were not different between the groups. LBGI and the number of hypoglycaemic events were not affected by the method of injection. BGRI were significantly higher for post-meal injection, mainly due to increased hyperglycaemia (p=0.003). The increased HBGI and BGRI were more prominent in CSII (p=0.05). These differences were found for the 72-hour variability but not when testing 2 hours post-prandially. It was concluded that injecting insulin prior to the meal can reduce the overall glucose variability, and remains the preferred method of injection. Larger studies are needed in order to reinforce these results.