Comparison of Residual Kidney Function Assessment Between the Hemodialysis 2-Day and 3-Day Interdialytic Interval

Abstract

Key Points There was no detected difference in measured residual kidney function between the short and long interdialytic intervals.Sample collection for assessment of residual kidney function can occur at either interdialytic interval without concerns surrounding comparability of results. Background Residual kidney function (RKF) is a dynamic marker having been shown to demonstrate fluctuations over successive days of the interdialytic interval. This study compares measured RKF between the long interdialytic interval (LIDP) and short interdialytic interval (SIDP). Methods This was a prospective cohort study. Thirty-four clinically stable, ambulatory facility hemodialysis patients were recruited. Urine samples collected in the last 12 hours of each interdialytic interval were paired with a blood test at the conclusion of each 12-hour interval to evaluate measured RKF through a mean of urinary urea and creatinine clearances. The paired Student t test and the Wilcoxon matched pairs signed-ranks were used, respectively, to compare differences in assessed mean and median RKF. Results Although average serum creatinine (607±219 µmol/L versus 547±192 µmol/L, P = <0.01) and serum urea concentrations (25±15 mmol/L versus 19±5 mmol/L, P = 0.01) were higher in the LIDP compared with SIDP, there was no statistically significant difference in urine volume (630±460 ml versus 520±470 ml, P = 0.06), urine urea (116±49 mmol/L versus 118±90 mmol/L, P = 0.87), or urine creatinine (7816±3943 µmol/L versus 8926±5752 µmol/L, P = 0.06) concentrations. On the whole, there was no significant difference in assessed RKF between the LIDP and SIDP (mean 8±6 ml/min versus 6±4 ml/min, P = 0.24; median 6.3 [3.2–10.4] versus 5.8 [3.8–8.9], P = 0.13). Conclusions There was no statistically significant difference observed in assessed RKF between the LIDP and SIDP. Measured RKF through samples collected from the LIDP and SIDP is comparable.