Linear Association Between Household Income and Metabolic Control in Children With Insulin-Dependent Diabetes Mellitus Despite Free Access to Health Care

Background: In health care systems with a user fee, the impact of socioeconomic factors on pediatric insulin-dependent diabetes mellitus (IDDM) control could be due to the cost of accessing care. Hypothesis: There is a linear association between household income and the average glycosylated hemoglobin (HbA1c) of children and adolescents with IDDM despite free access to health care. Methods: We used a linear regression model to examine the association between normalized average HbA1c of 1766 diabetic children (diagnosed at our institution from 1980 to 2011 before 17 years of age) and the median household income of their neighborhoods (obtained from Statistics Canada, 2006 Census data). Results: We found a negative linear association (P < .001; r = -0.2) between the level of income and metabolic control assessed by HbA1c after controlling for sex, age at diagnosis, duration of diabetes, ethnicity, geographical factors, frequency of visits, current age (as a proxy for change in practice over time), and change of measurement methods of HbA1c across time. For every increase of $15 000 in annual income, HbA1c decreased by 0.1%. Conclusion: We report a linear association of household income with metabolic control of IDDM in childhood. Given that Canada has a system of free universal access to health care, confounding by access to care is unlikely. Considering the impact of poorly controlled IDDM in childhood on the development of long-term complications, our findings suggest that the higher complication rate found in adults of low socioeconomic status might originate from the poor control that they experienced in childhood. Support for the care of IDDM children from low-income neighborhoods should be increased.