The importance of residual kidney function in haemodialysis patients.

In contrast to peritoneal dialysis, residual kidney function (RKF) is commonly disregarded for haemodialysis (HD) patients and not regularly monitored or taken into account in routine clinical care. This is despite evidence that higher levels of RKF in HD patients are associated with better outcomes, including survival, total solute clearance, nutrition, inflammation and fluid balance. This review aims to summarise the clinical effects of RKF specifically in HD patients. Some level of RKF is present in over 80% of patients at the time of dialysis initiation, and while this declines over time, up to 30% of patients on HD for 5 years still have a measurable level of native kidney function. There is little evidence on how best to preserve RKF in HD patients, although it has been observed that intensive HD regimens in incident HD patients appear to accelerate RKF decline. RKF is not commonly factored into HD prescription and measures of adequacy, despite the fact that some guidelines such as Kidney Disease Outcomes Quality Initiative (KDOQI) and European Best Practice Guidelines suggest that it is reasonable to do so. This likely relates, at least in part, to perceived concerns regarding the inconvenience of timed urine collections and to the complexity and lack of consensus regarding the methods for integrating the intermittent clearance of HD with the continuous clearance of native renal function. Further research is required into how best to maintain and maximise the benefits of RKF in HD patients.