Impact of the preservation of residual kidney function on hemodialysis survival: results from the BISTRO trial

Background: Preservation of residual kidney function (RKF) in dialysis patients has been associated with improved survival. RKF in the BISTRO trial was relatively well preserved and here we describe its association with survival during the trial and extended follow-up.
Methods: RKF, measured as the average urea and creatinine clearance (GFR) or 24-hour urine volume was assessed at baseline, one, two and three months and three-monthly up to 2 years in incident haemodialysis patients. Time to event survival data or competing events (transplantation, modality change) were obtained for 50 months post enrolment via data linkage with the UK Renal Registry. Cox proportional hazards regression survival models, including those incorporating change in GFR from baseline as a time-varying variable and joint regression models for longitudinal and survival data (longitudinal models for GFR or urine volume) were used to explore the relationship of RKF preservation with survival. Analyses were adjusted for age, sex, comorbidity and ethnicity.
Results: 2919 measures of RKF were made in 387 patients from 32 UK dialysis units. Higher age and comorbidity score associated with increased mortality in all models. Baseline GFR reduced the risk of death (Hazard Ratio: 0.918 95%CI: 0.844, 0.999) per ml/min/1.73m2. A greater fall in GFR and urine volume from baseline was associated with a non-significant increased risk of death as visualised on spline plots. In the joint survival models higher GFR (adjusted HR: 0.88 95%CI 0.80, 0.97) or urine volume (adjusted HR: 0.75 95%CI 0.57, 0.95 per L) at any time point associated with better survival.
Conclusions: Lower RKF during the first two years of haemodialysis is associated with an increased death risk for up to 50 months following dialysis initiation. This adds to a growing body of evidence that interventions to preserve RKF should be developed and tested in clinical trials.