Longitudinal Changes in Kidney Solute Clearance in a Prospective Cohort of Patients Initiating Chronic Hemodialysis

Abstract

IntroductionLongitudinal changes in residual kidney function (RKF) have not been well examined in patients started on chronic hemodialysis (HD). MethodsWe analyzed urine volume and kidney solute clearances from timed urine collections and corresponding plasma samples from 42 patients randomized to incremental HD (n=21) and conventional HD (n=21) in the TwoPlus study. Samples were collected prior to HD initiation (baseline); and at 6, 12, 24 and 48 weeks. We assessed temporal trends in urine volume, kidney urea clearance, and kidney creatinine clearance, and correlations between urine volume and kidney urea and creatinine clearances. ResultsRKF parameters in all patients declined over time; the pattern of decline differed between urine volume and kidney solute clearances. Urine volume declined at a steady rate with median (quartile 1, quartile 3) % change relative to baseline of -10% (-36, 29) at week 6 and -47% (-76, 5) by week 48. Kidney urea and creatinine clearances exhibited a larger decline than urine volume at week 6, -32% (-61, 8) and -47% (-57, -20), respectively. The rate of decline subsequently slowed, reaching about 61% decline for both solutes by week 48. Conventional HD demonstrated larger declines in urine volume and kidney urea clearance than incremental HD at week 6. Urine volume showed moderate correlation with urea (R=0.47) and weaker correlation with creatinine (R=0.34). ConclusionDespite gradual decrement in urine volume and kidney solute clearances, RKF persists nearly 1 year after HD initiation. This knowledge could motivate increased practice of individualizing HD prescriptions by incorporating RKF.