A new assessment tool to measure the ability of Bolus Calculation and Carbohydrate Estimation (SMART) in people with diabetes performing an intensive insulin therapy

Abstract

Background and aims: Intensive insulin therapy relies on correct prandial insulin dose adaptation dependent from current glucose level, amount of planned carbohydrate intake and the consideration of other situational factors like physical activity or circadian fluctuation of insulin sensitivity. People with diabetes and intensive insulin therapy should be able to estimate carbohydrates and calculate insulin bolus correctly, while regarding the factors mentioned above. An assessment tool for the measurement of the ability of carbohydrate estimation and bolus calculation is missing. The objective of this study was the development and psychometric evaluation of an assessment tool for carbohydrate estimation and bolus calculation (“aSsessMent of the Ability of Bolus Calculation and CaRbohydrate esTimation” SMART). Of special interest were the associations of both abilities with glycaemic control. Materials and methods: The SMART consisted of one scale for the assessment of bolus calculation (BOLUS) with 10 items and a scale for carbohydrate estimation (CARB) with 12 items. People with type 1 or type 2 diabetes on an intensive insulin regimen were invited to participate. HbA1c and stored data of blood glucose meters were used to determine glycaemic control. Results: 411 patients participated (age 42.9 ±15.7, 58% female, HbA1c 8.6 ±1.8%, 28% with CSII-treatment) and approx. 56,000 blood glucose meter readings could be obtained. The reliability of both scales was sufficient (Cron-bachs alpha for BOLUS r= 0.78 and the CARB r = 0.67). Better bolus calculation was associated with a higher level of education (r = 0.24, p<.05), lower HbA1c (r = -0.27, p<.05), lower mean blood glucose (r = -0.29, p<.05), and a lower standard deviation of blood glucose values (r = -0.43, p<.05). Better carbohydrate estimation was associated with a lower body mass index (r = -0.2, p<.05), lower mean blood glucose (r = -0.3, p<.05), a lower frequency of hyperglycaemia (r = -0.27, p<.05), and a higher frequency of euglycaemia (r = 0.26, p<.05). Patients with an insulin pump were better on both scales than patients with multiple daily insulin injections (BOLUS: 7.2 ± 2.4 vs. 6.4 ± 2.7, p<.01; CARB: 7.8 ± 2.1 vs. 7.1 ± 2.6, p<.01). Patients with previous diabetes education performed significantly better on both scales (BOLUS: 6.8 ± 2.5 vs. 5.7 ± 2.8, p<.01; CARB: 7.4 ± 2.4 vs. 6.5 ± 2.6, p<.01). Conclusion: SMART provides a reliable and valid assessment of the ability to estimate the correct amount of carbohydrates and to calculate the appropriate prandial insulin dose. SMART is also sensitive to depict effects of diabetes education and of CSII treatment in comparison to multiple daily insulin injections. In summary SMART can assist the identification of people with diabetes on an intensive insulin regimen, who are in need for improvements in carbohydrate estimation and/or calculation of prandial insulin dos