Choice of endpoint in kidney outcome trials: considerations from the EMPA-REG OUTCOME® trial

BACKGROUND: Doubling of serum creatinine equivalent to 57% reduction in estimated glomerular filtration rate (eGFR) is an established surrogate for end-stage kidney disease (ESKD); however, this endpoint necessitates lengthy follow-up and large sample sizes in clinical trials. We explored whether alternative eGFR decline thresholds provide more feasible surrogate kidney endpoints. METHODS: The study involved post hoc analysis of the EMPA-REG OUTCOME® trial. Adults with type 2 diabetes, high cardiovascular risk and eGFR ≥30 mL/min/1.73 m2 were assigned empagliflozin 10 mg or 25 mg (n = 4687) or placebo (n = 2333), on top of standard of care. We assessed composite endpoints incorporating different eGFR decline thresholds (≥30, ≥40, ≥50 or ≥57%) combined with initiation of renal replacement therapy (RRT) or renal death. This trial is registered with ClinicalTrials.gov (NCT01131676). RESULTS: Empagliflozin versus placebo significantly lowered the risk of decline in eGFR for each threshold listed above, combined with initiation of RRT or renal death, ranging from a hazard ratio (HR) of 0.81 95% confidence interval (CI) 0.72-0.91 for endpoints based on 30% eGFR decline to an HR of 0.37 (0.23-0.61) for endpoints based on 57% eGFR decline. Lower thresholds (e.g. 30%) were associated with higher event rates but weaker treatment effects. The time to the 95% CI of the HR falling to <1.0 decreased with increasing eGFR threshold. CONCLUSIONS: The composite of 40% decline in eGFR, ESKD or renal death appears to provide reliable results similar to the traditional 57% decline in eGFR.