in the previous issue of critical care , chou and colleagues   report that early initiation of renal replacement therapy ( rrt ) , as defined by rifle criteria , was not associated with reduction in hospital mortality in patients with acute kidney injury ( aki ) and sepsis . the timing of initiation of rrt has been a controversial issue for many years in both patients suffering from chronic kidney disease   and those suffering from acute kidney disease . a recently published systematic review and meta - analysis on this topic concluded that earlier initiation of rrt in critically ill aki patients may have a beneficial impact on survival but that , in the absence of new evidence from suitably designed randomized trials , a definitive treatment recommendation can not be made . the idea that ' earlier ' initiation of treatment should be beneficial stems from our belief that sometimes complex interventions may change the course of a disease . in the case of aki and sepsis , it has been hypothesized that early dialysis in sepsis can reduce circulating levels of inflammatory substances and may therefore beneficially impact on the pathophysiological mechanisms of the disease . unfortunately , the validity of this premise has never been proven , and existing evidence points rather in the opposite direction . both literature data and the currently published study once more confirm that patients with sepsis die with aki rather than of aki : no single indicator of renal function or kidney injury was predictive of mortality in the multivariate model as it was applied by chou and colleagues . in the patient group with septic aki , dialysis should not be seen as a curative intervention , but rather as supportive therapy , preventing the patient from dieing from hyperkalaemia or fluid overload during the period the kidneys are temporarily failing . as a consequence , early dialysis , in the semantic meaning of ' intervention before support is needed ' , exposes patients to side effects of the treatment without really helping them . problematic for correct interpretation of the data in nearly all studies , including the one by chou and colleagues , is the fact that virtually all are retrospective . this complicates the interpretation at various levels . as strict clinical rules on the timing of initiation of dialysis were present in these icus during the collection of these data , all patients in fact started at the same ' time point ' in their disease , that is , when they fulfilled one of the preset criteria . as such , the categorization ' early versus late ' loses the semantic significance of a ' time - related event ' , and in fact no conclusions on timing can be made . conclusions on the impact of ' early versus late initiation of dialysis ' would only be justified when , at the moment patients fulfilled the criteria for dialysis , one group started rrt immediately while for the other group dialysis was delayed for one or more days . in the only available randomized controlled trials in this field , early versus late was defined by the urinary output versus biochemical values   or by magnitude of urinary output . one important aspect of the current paper by chou and colleagues   is that the rifle criteria have no value in determining the need for dialysis , as equal numbers of patients within the different rifle categories were apparently started on dialysis . indeed , if rifle were a good predictor of need for dialysis , one would expect that there was a preponderance of rifle class ' i ' or ' f ' in the cohort of dialyzed patients , quod non . unfortunately , the study does not provide data on the distribution of the different rifle categories in the non - dialyzed patients , but we would not be surprised that these rifle categories were exactly comparable to those in the dialyzed cohort . rifle is a scoring system developed to grade prognosis of acute renal injury , and although it performs quite well at the cohort level , its applicability to individual patient outcome is rather poor . this is even more true in the current study , as the most powerful component of the rifle criteria , urine output , was not taken into account . as a consequence , the correct conclusion of the current data should thus be that serum creatinine is not a good parameter to use for determining when to start dialysis in aki patients , just as has been found in patients with chronic kidney disease . the omission of urine output as a parameter is critical , especially as fluid overload ( central venous pressure > 12 mmhg ) was a criterion to start dialysis . the combination of evaluation of fluid status and urine output , and especially the evolution over time of these two parameters , is probably one of the major decisive criteria to start dialysis at present . when the patient is euvolemic , or even volume overloaded , and still remains oliguric despite maximal support , one should not await further organ damage , and dialysis should be initiated . in addition , as only patients who did actually start dialysis were included , it is difficult to guess what happened to patients with classes rifle 0 or i who did not start dialysis . it is likely that these patients had a better survival than those who did start dialysis , and then , the conclusion of the study would be that early initiation of dialysis based on rifle criteria is detrimental . such a conclusion is different from the statement that early initiation of dialysis based on rifle criteria in patients with sepsis does not reduce mortality . in conclusion , maybe we can not answer this question now because it may be the wrong question : as dialysis is supportive and not curative , patients either need dialysis , in which case it should not be delayed , or they do not need dialysis , in which case it can only harm . once we have agreed on those , the timely initiation of dialysis in those who are predicted to inevitably progress to one of those conditions seems the most appropriate strategy . in contrast , with current practice , it seems unlikely that serum creatinine or another serum / urine - based biomarker will be one of those criteria .
earlier initiation of dialysis may have a beneficial impact on survival of critically ill patients with acute kidney injury ( aki ) . 
 a retrospective analysis in the previous issue of critical care showed that early initiation of renal replacement therapy ( rrt ) , as defined by rifle criteria , was not associated with a reduction in hospital mortality . 
 the retrospective character of many studies describing the results of early rrt initiation and the validity of rifle criteria to determine the need for dialysis can be questioned , in particular when urinary output is not considered . initiating dialysis in aki 
 should be based on clinical criteria and not on serum creatinine or another serum / urine - based biomarker .