Costs of people with diabetes in relation to average glucose control: an empirical approach controlling for year of onset cohorts

Objective To estimate the impact of glycaemic control and time since diabetes diagnosis on care costs incurred by people with type 2 diabetes mellitus (T2DM). Research design and methods Random-effects linear regression models were run to test the impact of average glucose control (HbA1c) and time since diabetes diagnosis on total care spending in people with T2DM, adjusting for year of onset and other covariates. Two datasets were linked, Vektis (healthcare costs reimbursed by the Dutch mandatory health insurance) and Zodiac (clinical and sociodemographic data). The sample includes 22,612 observations, grouped in 5653 individuals from the Northern part of the Netherlands, covering 4 years (2008-2011). Results A 1% point increase in HbA1c is associated with a 2.2% higher total care costs. However, when treatment modality is included, the results are modified. A 1% point increase (11 mol/mol) in HbA1c is significantly associated with 3.4% higher total care costs for individuals without glucose-lowering treatment. Being treated with insulin is significantly associated with an increase in costs of 30-38% for every additional percentage point of HbA1c, depending on the covariates included. Without controlling for year of onset, an additional year of diabetes duration relates to 2.6% higher care costs, while this is 4.9% controlling for year of onset. The effect of HbA1c and diabetes duration differs between types of costs. Conclusion HbA1c, insulin treatment and diabetes duration are the main drivers of increasing care costs. The results signal the relevance of controlling for HbA1c together with treatment modality, diabetes duration and year of diagnosis effects.