Besides, SOFA score was chosen as a representation of severity score for Cox analysis in our study. The predictive value for poor prognosis in AKI of SOFA score has been reported in other studies [1,30] as well.Similar to the enough report of a systemic review and meta-analysis summarizing all studies published before 2008 [9], our data supported the survival benefit in earlier initiation of RRT. However, discordant results existed. Bagshaw and colleagues [46] designed a prospective multicenter observational study enrolling 1238 patients to evaluate the relation between timing of RRT initiation in severe AKI and prognoses. Timing of RRT was assessed by several approaches such as median value and median change of BUN and sCr, and the period from ICU admission to start of RRT.

Contrary to our findings, they found late RRT stratified by median sCr was associated with lower mortality. Previous studies [47] using sCr criterion to define early RRT also failed to show survival benefit. The main plausible explanation is that low sCr levels might not necessarily represent a better residual renal function. In contrast, the low sCr could be a marker of reduced muscle mass and malnutrition, and it may be a surrogate marker of volume overload, which in turn might contribute to poor survival [33,46].However, this bias did not exist in our study because the sCr and albumin level were not statistically different between ED and LD groups upon ICU admission and before RRT initiation (Table (Table2).2). In fact, the relation between sCr and mortality was ever documented to be paradoxical in dialysis patients, which is called ‘reverse epidemiology’.

It refers to paradoxical and counter-intuitive epidemiologic associations between survival outcomes and traditional risk factors such as creatinine [48].It is worthy of mention that the LD group in our study has better baseline renal function (less CKD proportion, lower baseline sCr, higher baseline GFR) but worse pre-RRT renal function. There is no doubt that a larger sCr increase or GFR decrease categorized patients into LD group, but it also gave a hint that those with more sever renal function deterioration have poorer outcome. Actually, both the proportional change of sCr or GFR in RIFLE classification, and the absolute sCr level in the SOFA scores could predict prognoses in our patients.

This finding was supported by Coca and colleagues [49] who had disclosed the prognostic importance of a small acute change in sCr in absolute level as well as percentage changes.Limitations and summarySeveral limitations for this study should be recognized. First, Batimastat the limited patient number may not be large enough to determine other risk factors for in-hospital mortality. Second, only GFR criterion of RIFLE classification was used in the current study.