BACKGROUND:High ultrafiltration rate (UFR) has been associated with increased mortality in hemodialysis (HD) patients. However, the impact of UFR on decline of residual kidney function (RKF) has not been elucidated among patients receiving conventional HD. METHODS:We performed a retrospective cohort study of 7,753 patients who initiated conventional HD from 2007 to 2011 and survived the first year of dialysis with baseline UFR and renal urea clearance (KRU) data at baseline and 1 year (5th patient-quarter). The primary exposure was average UFR at the 1st patient-quarter from dialysis initiation (<4, 4 to <6, 6 to <9, 9 to <13, and ≥13 mL/h/kg). Decline in RKF was defined as the percent change in KRU and decline in urine output during the first year after initiation of dialysis. We used a logistic regression model for rapid decline in RKF and a linear regression model for change in urine volume. RESULTS:In our HD cohort, mean baseline UFR was 7.0 ± 3.1 mL/h/kg, and median (interquartile range) baseline KRU was 3.5 (2.1-5.3) mL/min/1.73 m2. There was a graded association between UFR and a rapid decline in RKF; the expanded case mix-adjusted ORs and 95% CIs were 1.21 (1.04-1.40), 1.34 (1.16-1.55), 1.73 (1.46-2.04), and 1.93 (1.48-2.52) for baseline UFR 4 to <6, 6 to <9, 9 to <13, and ≥13  mL/h/kg, respectively (reference: <4 mL/h/kg). KRU trajectories showed a greater KRU decline over time in higher UFR categories. Higher UFR was also associated with a greater decline in urine output after 1 year. CONCLUSION:Higher UFR was associated with a rapid decline in RKF among conventional HD patients. Further clinical trials are needed to elucidate a causal effect of UFR on RKF among HD patients.