Changes in HbA1c during the first six years after the diagnosis of Type 2 diabetes mellitus predict long-term microvascular outcomes.

To analyze the association between change in HbA1c during the first 6 years after diagnosis of Type 2 diabetes mellitus (Type 2 DM) and incident micro- and macrovascular morbidity and mortality during 13 years thereafter. This is an observational study of the participants in the intervention arm of the randomized controlled trial Diabetes Care in General Practice (DCGP) in Denmark. 494 newly diagnosed persons with Type 2 DM aged 40 years and over with three or more measurements of HbA1c during six years of intervention were included in the analyses. Based on a regression line, fitted through the HbA1c-measurements from 1 to 6 years after diabetes diagnosis, glycaemic control was characterized by the one-year level of HbA1c after diagnosis, and the slope of the regression line. Outcomes were incident diabetes-related morbidity and mortality from 6 to 19 years after diabetes diagnosis. The association between change in HbA1c (the slope of the regression line) and clinical outcomes were assessed in adjusted Cox regression models. The median HbA1c level at year one was 60 (IQR: 52-71) mmol/mol or (7.65 (IQR: 6.91-8.62) %). Higher HbA1c levels one year after diagnosis were associated with a higher risk of later diabetes-related morbidity and mortality. An increase in HbA1c during the first 6 years after diabetes diagnosis was associated with later microvascular complications (HR per 1.1 mmol/mol or 0.1% point increase in HbA1c per year; 95% CI) = 1.14; 1.05-1.24). Change in HbA1c did not predict the aggregate outcome 'any diabetes-related endpoint, all-cause mortality, diabetes-related mortality, myocardial infarction, stroke, or peripheral vascular diseases. We conclude that suboptimal development of glycaemic control during the first 6 years after diabetes diagnosis was an independent risk factor for microvascular complications during the succeeding 13-year follow-up, but not for mortality or macrovascular complications.