Measuring residual renal function for hemodialysis adequacy: Is there an easier option?

Most patients starting hemodialysis (HD) have residual renal function. As such, there has been increased interest in starting patients with less frequent and shorter dialysis session times. However, for this incremental approach to be successful, patients require regular monitoring of residual renal function, so that as residual renal function declines, the amount of HD is appropriately increased. Currently most dialysis centers rely on interdialytic urine collections. However, many patients find these inconvenient and there may be marked intrapatient variability due to compliance issues. Thus, alternative markers of residual renal function are required for routine clinical practice. Currently three middle sized molecules; cystatin C, β2 microglobulin, and βtrace protein have been investigated as potential endogenous markers of glomerular filtration. Although none is ideal, combinations of these markers have been proposed to provide a more accurate estimation of glomerular clearance, and in particular cut offs for minimal residual renal function. However, in patients with low levels of residual renal function it remains unclear as to whether the benefits of residual renal function equally apply to glomerular filtration or tubular function.