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

Background. We aimed to explore the relationship between serum bicarbonate( SBC) and mortality in advanced chronic kidney disease( 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 European QUALity Study on treatment in advanced CKD( EQUAL) cohort, which includes patients aged ≥65 years and estimated glomerular filtration rate( eGFR) ≤20 mL/min/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 1485 patients with a median follow-up of 2.9( interquartile range 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 = .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 = .01) . Similarly, in the KRT population, low SBC levels showed a trend towards increased mortality risk( P = .13) . We observed effect modification by subjective global assessment category( P -value for interaction = .02) and KRT( P -value for interaction = .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.