Urine volume as an estimator of residual renal clearance and urinary removal of solutes in patients undergoing peritoneal dialysis

Abstract

In non-anuric patients undergoing peritoneal dialysis (PD), residual kidney function (RKF) is a main contributor to fluid and solute removal and an independent predictor of survival. We investigated if urine volume could be used to estimate renal clearances and removal of urea, creatinine, and phosphorus in PD patients. The observational, cross-sectional study included 93 non-anuric prevalent PD patients undergoing continuous ambulatory PD (CAPD; n = 34) or automated PD (APD; n = 59). Concentrations of urea, creatinine and phosphorus in serum and in 24-h collections of urine volume were measured to calculate weekly residual renal clearance (L/week) and removed solute mass (g/week). Median [interquartile range], 24-h urine output was 560 [330–950] mL and measured GFR (the mean of creatinine and urea clearances) was 3.24 [1.47–5.67] mL/min. For urea, creatinine and phosphorus, residual renal clearance was 20.60 [11.49–35.79], 43.02 [19.13–75.48] and 17.50 [8.34–33.58] L/week, respectively, with no significant differences between CAPD and APD. Urine volume correlated positively with removed solute masses (rho = 0.82, 0.67 and 0.74) and with weekly residual renal clearances (rho = 0.77, 0.62 and 0.72 for urea, creatinine, and phosphorus, respectively, all p < 0.001). Residual renal clearances and urinary mass removal rates for urea, creatinine, and phosphorus correlate strongly with 24-h urine volume suggesting that urine volume could serve as an estimator of typical values of residual solute removal indices in PD patients.

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

“…showed that urine volume correlated with the kidney clearances of urea, creatinine, and phosphorus. 26 In our study, that was comprised solely of patients treated with HD, we noted a weaker correlation between the urine volume and residual kidney urea and creatinine clearances. However, comparisons are difficult to undertake given differences in metabolic dynamics and extracorporeal clearances between peritoneal dialysis and HD.…”

Clinical significance of serum urea‐to‐creatinine ratio in patients undergoing peritoneal dialysis

“…RKF is one of the most important indicators for maintaining optimal dialysis efficiency in patients on PD [2], and it has been linked to a variety of outcomes, including life expectancy, cardiovascular mortality, blood pressure (BP), anemia, chronic inflammation, and serum phosphorus management [3]. Measuring renal Kt/V and CCr remains the standard clinical index for assessing RKF in patients on PD [4,5]. However, accurate evaluation requires a 24-h collection of urine and PD fluid, which is difficult to perform, particularly in patients on assisted PD and the elderly.…”