Estimating Residual Kidney Function: Present and Future Challenge

Abstract

Residual kidney function is a major prognosis factor in patients with end-stage renal disease under hemodialysis or peritoneal dialysis. Advances in later years promoted residual kidney function protection as an adequacy target and the advocacy of incremental dialysis, utilizing its assessment as a parameter of individualized dialysis schedules. Glomerular filtration rate measurement is only a dimension of kidney function neglecting the share of tubular function, with several dialytic limitations. The need for interdialytic urine collections to quantify residual kidney function, by the mean of urea and creatinine clearances, is cumbersome and prone to errors in dialysis patients. This review will approach residual kidney function estimation without urine collection, mainly with biomarkers such as cystatin C, beta-2 microglobulin, and beta-trace protein, as well as the behavior of these molecules on various dialysis modalities, their non-renal determinants, and its potential use for patient risk stratification. Multi-frequency bioimpedance analysis is also described as a promising approach to estimate residual kidney function, being an opportunity to highlight the relevant link between volume balance and diuresis. We conclude that standard glomerular filtration rate estimation formulas are not sufficiently accurate for residual kidney function assessment. There is a need for innovative tools that consider glomerular and interstitial function to be implement in clinical practice, therefore the new equations already developed and approached in this review should be validated in larger cohorts.