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

Abstract

Background and objectives: Residual kidney function can be assessed by simply measuring urine volume, calculating GFR using 24-hour urine collection, or estimating GFR using the proposed equation (eGFR). We aimed to investigate the relative prognostic value of these residual kidney function parameters in patients on dialysis.

Design, setting, participants, & measurements: Using the database from a nationwide prospective cohort study, we compared differential implications of the residual kidney function indices in 1946 patients on dialysis at 36 dialysis centers in Korea between August 1, 2008 and December 31, 2014. Residual GFR calculated using 24-hour urine collection was determined by an average of renal urea and creatinine clearance on the basis of 24-hour urine collection. eGFR-urea, creatinine and eGFR β₂-microglobulin were calculated from the equations using serum urea and creatinine and β₂-microglobulin, respectively. The primary outcome was all-cause death.

Results: During a mean follow-up of 42 months, 385 (19.8%) patients died. In multivariable Cox analyses, residual urine volume (hazard ratio, 0.96 per 0.1-L/d higher volume; 95% confidence interval, 0.94 to 0.98) and GFR calculated using 24-hour urine collection (hazard ratio, 0.98; 95% confidence interval, 0.95 to 0.99) were independently associated with all-cause mortality. In 1640 patients who had eGFR β₂-microglobulin data, eGFR β₂-microglobulin (hazard ratio, 0.98; 95% confidence interval, 0.96 to 0.99) was also significantly associated with all-cause mortality as well as residual urine volume (hazard ratio, 0.96 per 0.1-L/d higher volume; 95% confidence interval, 0.94 to 0.98) and GFR calculated using 24-hour urine collection (hazard ratio, 0.97; 95% confidence interval, 0.95 to 0.99). When each residual kidney function index was added to the base model, only urine volume improved the predictability for all-cause mortality (net reclassification index =0.11, P=0.01; integrated discrimination improvement =0.01, P=0.01).

Conclusions: Higher residual urine volume was significantly associated with a lower risk of death and exhibited a stronger association with mortality than GFR calculated using 24-hour urine collection and eGFR-urea, creatinine. These results suggest that determining residual urine volume may be beneficial to predict patient survival in patients on dialysis.

Keywords: dialysis; end-stage renal disease; glomerular filtration rate; mortality; residual kidney function; urine volume.

Figure 1.

Among 5175 initially enrolled patients with ESRD on dialysis therapy, 1946 patients were finally analyzed. CRC for ESRD, Clinical Research Center for End-Stage Renal Disease; RKF, residual kidney function.

Figure 2.

Among three residual kidney function (RKF) indices, only residual urine volume (UV) indicated an independent prognostic value in patients with UV≥0.1 or <0.1 L/d, patients on hemodialysis, patients on peritoneal dialysis, and patients with dialysis vintage <2 or ≥2 years. Adjusted hazard ratios (HRs) were calculated after adjustment for age, sex, dialysis modality, dialysis vintage, modified Charlson comorbidity index, smoking status, and serum albumin concentrations. In subgroup analysis regarding hemodialysis and peritoneal dialysis, dialysis modality was not adjusted. Similarly, in subgroup analysis regarding patients with dialysis duration <2 and ≥2 years, dialysis vintage was not adjusted. 95% CI, 95% confidence interval; eGFR-urea,creat, estimated GFR calculated from the serum and creatinine concentrations; GFR-24U, GFR by 24-hour urine collection.