All-cause mortality in relation to glycated haemoglobin in individuals with newly diagnosed type 2 diabetes: a retrospective cohort study

Aims: To explore the effect of glycated haemoglobin A1C (HbA1C) on all cause mortality in individuals newly diagnosed with type 2 diabetes, with and without previous cardiovascular disease. Methods: We identified a total of 110,372 of individuals aged 18 to 80 years newly diagnosed with type 2 diabetes (including 9721 (8.8%) with established cardiovascular disease before diagnosis of diabetes) from the UK General Practice Research Database from 1990 to 2005. Primary outcome was all cause mortality. Cox proportional hazards models were used to assess the impact of HbA1C on survival. Results: Over a median follow up of 5.2 years (interquartile range 2.9 to 8.1 years) there were 20,481 deaths. The hazard ratios for all cause mortality in individuals without cardiovascular disease, using the category of 6–6.49% as reference, were 1.28 (1.08 to 1.52), 1.16 (1.00 to 1.39), 1.43 (1.20 to 1.72), 1.62 (1.35 to 1.95), 1.80 (1.52 to 2.23), and 2.43 (2.01 to 2.97) for HbA1C categories of < 6.0%, 6.50–6.99%, 7.0–7.49%, 7.5–7.99%, 8.0–8.99%, and > 9.0% respectively. In individuals with established cardiovascular disease a significant increased risk of mortality was observed for HbA1C categories above 8.00%; hazard ratios 1.91 (1.30–2.83) for HbA1C 8.00–8.99% and 1.95 (1.30–2.90) for HbA1C > 9.0%. Conclusions: A target of HbA1C between 6.0 and 6.5% is appropriate for individuals newly diagnosed with type 2 diabetes without cardiovascular disease. However, a target of < 8.0% may be less beneficial in individuals with established cardiovascular disease.