RCS plots of the relationship between Uprot (top) and F-Uprot (bottom) and ESRD by CKD stage where effect was nonlinear. Lines indicate the HR estimates. Uprot reference level is 0.15 g/24 h. F-Uprot reference level is 1 g/24 h per 100 mL/min/1.73 m² eGFR. HRs are stratified by cohort and CKD stage and adjusted for all variables in Table 2. P-values for Uprot: <0.001 for Stage G3b, <0.001 for Stage G4. P-values for F-Uprot: <0.001 for Stage G3b, <0.001 for Stage G4 and 0.048 for Stage G5.