Early versus late renal replacement therapy in acute kidney injury: the search for a definition of timing continues

and colleagues on early versus late renal replacement therapy (RRT) in critically ill patients with acute kidney injury (AKI) [1]. Th e authors rightly cite enormous heterogeneity between the 15 studies reviewed as a key concern. We would like to focus on the varied approach and lack of consensus in defi ning early and late initiation of RRT, as all of the 15 studies quote diff erent defi nitions in their methods. Even those utilising similar markers and criteria for AKI – for example, the RIFLE criteria [2] (two studies) or blood urea and nitrogen (four studies) – utilised and interpreted them in very diff erent ways when distinguishing early and late initiation of RRT. None of the studies reviewed used the Acute Kidney Injury Network (AKIN) criteria [3]. Having applied the AKIN criteria to data from our 20-bed critical care unit for all patients receiving RRT in 2009 (n = 158), we also failed to show RRT initiated at an early stage of AKI to be of benefi t in terms of critical care or hospital survival. Figure 1 shows a higher rate of hospital mortality in patients with AKIN stage 1 AKI (P = 0.01). Patient charac teristics including age, sex and Acute Physiology and Chronic Health Evaluation scores were similar across all groups. In view of our experience and Karvellas and colleagues’ conclusions, surely the matter of greatest urgency prior to any multicentre trial is establishing a satisfactory defi nition for early and late initiation of RRT.