Estimating residual kidney function in dialysis patients without urine collection

Abstract

Residual kidney function contributes substantially to solute clearance in dialysis patients but cannot be assessed without urine collection. We used serum filtration markers to develop dialysis-specific equations to estimate urinary urea clearance without the need for urine collection. In our development cohort, we measured 24-hour urine clearances under close supervision in 44 patients and validated these equations in 826 patients from the Netherlands Cooperative Study on the Adequacy of Dialysis. For the development and validation cohorts, median urinary urea clearance was 2.6 and 2.4 mL/min, respectively. During the 24-hour visit in the development cohort, serum β-trace protein concentrations remained in steady state but concentrations of all other markers increased. In the validation cohort, bias (median measured minus estimated clearance) was low for all equations. Precision was significantly better for β-trace protein and β2-microglobulin equations and the accuracy was significantly greater for β-trace protein, β2-microglobulin and cystatin C equations, compared with the urea plus creatinine equation. Area under the receiver operator characteristic curve for detecting measured urinary urea clearance by equation-estimated urinary urea clearance (both 2 mL/min or more) were 0.821, 0.850 and 0.796 for β-trace protein, β2-microglobulin and cystatin C equations, respectively; significantly greater than the 0.663 for the urea plus creatinine equation. Thus, residual renal function can be estimated in dialysis patients without urine collections.

Prognostic Value of Residual Urine Volume, GFR by 24-hour Urine Collection, and eGFR in Patients Receiving Dialysis

“…Fifth, new filtration markers, such as cystatin C and b-trace protein, were not available in our cohort. Recent studies proposed an equation using these markers without urine collection (26,35). Furthermore, precision and accuracy of b-trace protein, B2M, and cystatin C equations were significantly greater than for the urea-or creatinine-based equation (26).…”

“…Recent studies proposed an equation using these markers without urine collection (26,35). Furthermore, precision and accuracy of b-trace protein, B2M, and cystatin C equations were significantly greater than for the urea-or creatinine-based equation (26). However, additional relatively expensive cost limits measurement of these markers in routine practice of dialysis units; b-trace protein assay is available only for research purposes in Korea.…”

“…RKF can be determined by GFR derived from the renal clearance of urea and creatinine or the average of urea and creatinine using 24-hour urine collection (GFR-24U) or residual urine volume (UV) (24,25). Without urine collection, equations for eGFR using serum filtration markers have been proposed in patients on dialysis (26).…”

Increasing Haemodialytic Clearances as Residual Renal Function Declines: An Incremental Approach

“…Thus, there has been renewed interest in trying to develop serum-based RRF assessments. Two equations have been recently proposed, using serum biomarkers including β2M, β-trace protein and cystatin C [42,43] and have been validated as a pragmatic technique for estimating RRF, and developing this approach will allow more dialysis centres offer an incremental dialysis approach.…”

“…However, practising incremental dialysis without adjusting dialytic clearance potentially only leads to greater morbidity and mortality [10,42]. Appropriate patient selection, for instance, baseline urea clearance >3 mL/min/1.73 m 2 or urine volume >600 mL/day [10], should be the first step to consider whether patients may be suitable for incremental dialysis before applying this regime to prevent further complications (Table 1).…”