Residual renal function at the start of dialysis and clinical outcomes

Background. This study evaluates the association between estimated GFR (eGFR) at the start of dialysis and mortality within Europe. Methods. Renal registries participating in the ERA-EDTA Registry were asked to provide data on serum creatinine recorded 0-4 weeks before the start of dialysis in incident dialysis patients in 1999 and 2003. Within this cohort study, data were available in 11 472 patients from nine national or regional European renal registries. Cox regression analyses were performed to examine the association between GFR estimated by the four-variable MDRD equation (eGFR) and all-cause mortality, using a follow-up through 31 December 2005. Results. In the 2003 data, the mean eGFR was 8.6 ml/min/1.73 m(2). The unadjusted survival analyses showed that an increase in eGFR of 1 ml/min/1.73 m(2) was associated with a higher mortality risk (HR = 1.03; 95% CI: 1.03-1.04) that remained similar after adjustment for age, gender, primary renal disease, treatment modality, country and comorbidity. The findings were consistent across gender, treatment modalities, geographical regions and time periods (2003 versus 1999), but the association between a higher eGFR at the start of dialysis and mortality was the strongest in the youngest age groups and in patients with glomerulonephritis. Analyses at centre level showed that a 10% increase in the percentage of patients starting dialysis at high eGFR levels (>= 10.5 ml/min) was associated with a 22% higher mortality risk (HR = 1.22; 95% CI: 1.18-1.26). Conclusions. This European study showed that a higher eGFR at the start of dialysis was associated with a higher mortality risk. However, an answer to the question when to start dialysis needs to come from randomized controlled trials.