Serum urea concentration is probably not related to outcome in ICU patients with AKI and renal replacement therapy

Background. Acute kidney injury (AKI) is a common complication in patients admitted to the intensive care unit (ICU). Among other variables, serum urea concentrations are recommended for timing of initiation of renal replacement therapy (RRT). The aim of this study was to evaluate whether serum urea concentration or different serum urea concentration cutoffs as recommended in the literature were associated with in-hospital mortality at time of initiation of RRT for AKI. Methods. This is a retrospective single-centre study during a 3-year period (2004-07), in a 44-bed tertiary care centre ICU of adult AKI patients who were treated with RRT. Results. Three hundred and two patients were included: 68.9% male, median age 65 years and an APACHE II score of 21. The overall in-hospital mortality was 57.9%. Non-survivors were older (67 versus 64 years, P = 0.016) and had a higher APACHE II score (22 versus 20, P < 0.001). At time of initiation of RRT, they were more severely ill and had a lower serum urea concentration compared to survivors (130 versus 141 mg/dL, P = 0.038). Serum urea concentration, as well as the different historical serum urea concentration cut-offs had low area under the curves for the receiver operating characteristic curve for prediction of mortality. In multivariate analysis, age, and at time of initiation of RRT, potassium, SOFA score with exclusion of points for AKI and RIFLE class were associated with mortality, but serum urea concentration and the different cut-offs were not. Conclusions. This retrospective study suggests that serum urea concentration and serum urea concentration cut-offs at time of initiation of RRT have no predictive value for in-hospital mortality in ICU patients with AKI.