Impact of differing glucose-lowering regimens on the pattern of association between glucose control and survival.

Aims: To characterize survival in relation to achieved glycated haemoglobin (HbA1c) level within alternative glucose-lowering regimens with differing risks of hypoglycaemia.

Methods: Data were extracted from the UK Clinical Practice Research Datalink and the corresponding Hospital Episode Statistics. Patients with type 2 diabetes prescribed glucose-lowering therapy in monotherapy or dual therapy with metformin between 2004 and 2013 were identified. Risk of all-cause mortality within treatment cohorts was evaluated using the Cox proportional hazards model, introducing mean HbA1c as a quarterly updated, time-dependent covariable.

Results: There were 6646 deaths in a total follow-up period of 374 591 years. Survival for lower (<7%) vs moderate HbA1c levels (≥7%, <8.5%) differed by cohort: metformin, adjusted hazard ratio (aHR) 1.03 (95% confidence interval [CI] 0.95-1.12); sulphonylurea, aHR 1.11 (95% CI 0.99-1.25); insulin, aHR 1.47 (95% CI 1.25-1.72); combined regimens with low hypoglycaemia risk, aHR 1.02 (95% CI 0.94-1.10); and combined regimens with higher hypoglycaemia risk excluding insulin, aHR 1.24 (95% CI 1.13-1.35) and including insulin, aHR 1.28 (95% CI 1.18-1.37). Higher HbA1c levels were associated with increased mortality in regimens with low hypoglycaemia risk. Post hoc analysis by HbA1c deciles revealed an elevated risk of all-cause mortality for the lowest deciles across all cohorts, but particularly in those regimens associated with hypoglycaemia. High HbA1c was associated with no difference, or a small increase in mortality risk in regimens with increased risk of hypoglycaemia.

Conclusions: The pattern of mortality risk across the range of HbA1c differed by glucose-lowering regimen. Lower HbA1c was associated with increased mortality risk compared with moderate control, especially in those regimens associated with hypoglycaemia. High levels of HbA1c were associated with the expected elevated mortality risk in regimens with low hypoglycaemia risk.