MO703URINE VOLUME AS A MARKER OF RESIDUAL KIDNEY FUNCTION IN PERITONEAL DIALYSIS PATIENTS: QUANTITATIVE ASSESSMENT
Authors: Pinto Joyce , Debowska Malgorzata , Gomez Rafael , Waniewski Jacek , Lindholm Bengt 
Published: May 2021

Abstract

Background and Aims
In dialysis patients, urine volume is an easy-to-obtain marker of residual kidney function but information is lacking of its potential value as an estimate of the renal contribution to total clearance of small solutes. We explored whether correlations of urine volume with different estimations of the residual renal function for urea, creatinine, and phosphorus, could be used to assess renal solute clearances and renal mass removal for investigated solutes.

Method
In an observational study of 94 non-anuric (urine output ≥ 100 mL per 24 hours) patients (54% men, median age 59 [45 - 68] year, BMI 25.8 [21.4 - 27.7] kg/m2) undergoing automated (n = 59) or continuous ambulatory (n = 35) peritoneal dialysis (PD), we evaluated renal, peritoneal and total (renal plus peritoneal) solute removal (g/week) and clearance (L/week) in relation to urine volume (L/day). Urine volume, renal clearances, ratio of urine solute to serum solute concentration, removed mass of each solute and the ratio of mass removed by urine (renal clearance) over total mass removed by urine and dialysate (total clearance) for urea, creatinine and phosphorus were estimated from 24 h collections of urine and dialysate and determination of solute concentrations in serum, urine and dialysate. Statistical dependence between variables was tested using Spearman’s correlation coefficient (rho). Data are expressed as median with interquartile range.

Results
Median 24-hour urine output was 560 [323 – 938] mL. Renal mass removal for urea, creatinine and phosphorus was 10.1 [4.5 – 17.1], 3.5 [1.8 – 5.6] and 1.0 [0.4 – 1.7] g/week, respectively. The average contribution of residual renal removal to the total mass removed was 28% [17% - 41%] for urea, 56% [30% - 72%] for creatinine and 44% [24% - 58%] for phosphorus. Serum creatinine correlated weakly and negatively with urine volume (rho = -0.26, p &lt; 0.05), but no such relationship was observed for urea and phosphorus. Only urine concentration of creatinine correlated weakly with urine volume with rho = -0.28 and p &lt; 0.01. Urine concentration over plasma concentration did not correlate with urine volume for any solute. Renal urea clearance (20.1 [11.4 - 35.7] L/week) correlated positively with creatinine renal clearance (43.0 [18.9 - 75.1] L/week), (rho = 0.92), and with phosphorus renal clearance (17.3 [7.6 - 32.9] L/week), (rho = 0.89, p &lt; 0.001; Fig. 1A), while renal creatinine clearance correlated positively with phosphorus renal clearance (rho = 0.86, p&lt;0.001). Urine volume correlated positively with urea, creatinine and phosphorus clearances at rho 0.78, 0.63 and 0.73, respectively (all p&lt; 0.001), and with renal removal of mass of urea, creatinine, and phosphorus with rho= 0.83, 0.68 and 0.74 (Fig. 1B), respectively; all p&lt;0.001.

Conclusion
In PD patients, solute renal clearances and renal mass removal for urea, creatinine and phosphorus may be predicted from urine volume. Among renal clearances for urea, creatinine, and phosphorus two of them may be assessed based on measurements of the third one.