Background It has recently been suggested that mild renal dysfunction is associated with increased mortality in cardiac surgery; however, this risk factor is not accounted for in the European System for Cardiac Operative Risk Evaluation (EuroSCORE). The aim of the present study was to assess the effect of mild renal dysfunction as a predictor of operative mortality and develop and validate a modified logistic EuroSCORE model.

Methods This was a retrospective, observational, cohort study of prospectively collected data on 16 086 consecutive patients undergoing cardiac surgery at the Bristol Heart Institute between April 1996 and February 2009. To develop a modified logistic EuroSCORE, data were dived into developmental and validation datasets (11 596 and 4490 patients respectively). The relationship between risk factors and mortality was assessed using univariate and logistic regression analysis. Calibration and discrimination were assessed by Hosmer Lemeshow χ² test and receiving operative characteristic (ROC) curve.

Results Overall hospital mortality was 2.6%. At multivariate analysis, 13 out of 18 variables of the EuroSCORE influenced operative mortality; moreover, preoperative mild renal dysfunction, defined as serum creatinine 130–199 μmol/l, was identified as a new risk factor for mortality (OR 1.819, 95% CI 1.353 to 2.447, p<0.0001). EuroSCORE was able to predict mortality; however, modified logistic EuroSCORE had a better discriminatory power (area under ROC: 0.844 vs 0.784, p=0.002).

Conclusions Preoperative mild renal dysfunction is an independent risk factor for mortality in patients undergoing cardiac surgery. These findings now need to be validated with data from other centres.