Serum bicarbonate concentration and the risk of death in type 2 diabetes: the Fremantle Diabetes Study Phase II

Aims: To examine whether all-cause mortality is independently associated with serum bicarbonate concentration below the laboratory reference interval in a representative, well-characterised community-based cohort of people with type 2 diabetes. Methods: 1478 FDS2 participants with type 2 diabetes (mean age 65.8 years, 51.6% males, median diabetes duration 9.0 years) from the longitudinal, observational Fremantle Diabetes Study Phase II (FDS2) were followed from study entry to death or end-2016. Independent associates of a low baseline serum bicarbonate (< 22 mmol/L) were determined using multiple logistic regression. The role of important covariates in influencing the association between bicarbonate and mortality was assessed by a stepwise Cox regression approach. Results: A low serum bicarbonate was associated with increased all-cause mortality in unadjusted analysis (hazard ratio (HR) 1.90 (95% confidence limits (CL) 1.39, 2.60 per mmol/L). Mortality remained significantly associated with low serum bicarbonate (HR 1.40 (95% CL 1.01, 1.94) per mmol/L) in a Cox regression model with adjustment for factors associated with mortality but not low serum bicarbonate, but inclusion of estimated glomerular filtration rate categories rendered the association non-significant (HR 1.16 (95% CL 0.83, 1.63) per mmol/L). Conclusions: A low serum bicarbonate is not an independent prognostic marker in people with type 2 diabetes but it may be a manifestation of the pathway between the development of impaired renal function and death.