Longitudinal serum bicarbonate and mortality risk in older patients with advanced chronic kidney disease: analyses from the EQUAL cohort

Abstract

Background and hypothesis We aimed to explore the relationship between serum bicarbonate (SBC) and mortality in advanced CKD during three distinct treatment periods: during the pre-kidney replacement therapy (KRT) period, during the transition phase surrounding the start of KRT (transition-CKD), and during KRT. Methods Using the EQUAL cohort, which includes patients aged ≥ 65 years and eGFR ≤20 ml/min per 1.73 m2 from six European countries, we explored the association between longitudinal SBC and all-cause mortality in three separate CKD populations: pre-KRT, transition-CKD and in the KRT populations, using multivariable time-dependent Cox regression models. We evaluated effect modification by pre-specified variables on the relationship between SBC and mortality. Results We included 1 485 patients with a median follow-up of 2.9 (IQR 2.7) years, during which 529 (35.6%) patients died. A U-shaped relationship between SBC levels and all-cause mortality was observed in the pre-KRT population (P = 0.03). Low cumulative exposure, defined as the area under the SBC trajectory before KRT initiation, was associated with increased mortality risk after transitioning to KRT (P = 0.01). Similarly, in the KRT population, low SBC levels showed a trend towards increased mortality risk (P = 0.13). We observed effect modification by subjective global assessment (SGA) category (p-value for interaction = 0.02) and KRT (p-value for interaction = 0.02). Conclusions A U-shaped relationship describes the association between SBC and mortality in the advanced CKD pre-KRT population, whereas in the KRT population a trend towards an increased mortality risk was observed for low SBC levels.