Supplementary Material for: Starting Renal Replacement Therapy: Is It About Time?

Background: Studies of the timing of end-stage renal disease (ESRD) have primarily defined “early” versus “late” initiation of dialysis using estimated glomerular filtration rate (eGFR)-based criteria. Our objective was to determine the theoretical time that could be spent in chronic kidney disease (CKD) stage 5 prior to reaching a conservative eGFR threshold of 5 mL/min/1.73 m² compared to the actual time spent in CKD stage 5 by risk factors of interest. Methods: Eight-hundred and seventy Chronic Renal Insufficiency Cohort participants with CKD stage 5 who started renal replacement therapy (RRT) were included for retrospective study. We used mixed models to estimate the person-specific trajectory of renal function. We then used these individual trajectories to estimate the amount of time that would be spent in CKD stage 5 (between eGFR of 15 and 5 mL/min/1.73 m²) and compared this estimate to the actual time spent in CKD stage 5 prior to ESRD (between eGFR of 15 mL/min/1.73 m² and ESRD). Results: We found the median observed time between eGFR of 15 mL/min/1.73 m² to RRT was 9.6 months, but the median predicted time between eGFR of 15 mL/min/1.73 m² to eGFR of 5 mL/min/1.73 m² was 17.7 months. Some of the largest differences between the predicted and actual amount of time spent in CKD stage 5 were noted among those with systolic blood pressure <140 mm Hg (9.7 months longer predicted compared to actual), proteinuria <1 g/g (9.1 months), and serum albumin ≥3.5 g/dL (9.0 months). Conclusion: We found marked differences between the actual and predicted time spent in CKD stage 5 based on risk factors of interest. We believe that placing timing of dialysis initiation in the perspective of time is novel and may identify subgroups of patients who may derive particular benefit from a more concerted effort to delay RRT.