We read with interest the article by Grams et al1 assessing the incidence of and risk factors for acute kidney injury (AKI) after major surgery and the association of AKI with postoperative outcomes. In this study, the authors used appropriate statistical methods to identify risk factors for AKI and determine the association of baseline characteristics with AKI and the association of AKI with postoperative outcomes. However, we noted that the variables used for the modified Poisson regression model were baseline characteristics and surgery type only, but not known intra- and postoperative risk factors for AKI.