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

Background and objectives Residual kidney function can be assessed by simply measuring urine volume, calculatingGFRusing 24-hour urine collection, or estimatingGFRusing the proposed equation (eGFR). Weaimed to investigate the relative prognostic value of these residual kidney function parameters in patients on dialysis. Design, setting, participants,& measurementsUsing the database froma nationwide prospective cohort study, we compared differential implications of the residual kidney functionindices in 1946 patients ondialysis at 36dialysis 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 andeGFR beta(2)-microglobulinwere calculatedfromthe equationsusingserumurea and creatinine and beta(2)-microglobulin, respectively. The primary outcome was all-cause death. Results During amean follow-up of 42months, 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 beta(2)-microglobulin data, eGFR beta(2)-microglobulin (hazard ratio, 0.98; 95% confidence interval, 0.96 to 0.99) was also significantly associated with all-causemortality aswell 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 indexwas added to the basemodel, 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 volumewas significantly associated with a lower risk of death and exhibited a stronger associationwithmortality thanGFRcalculated 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.