In a recent published study (32) a cut-off for baseline serum creatinine and its influence on mortality after cardiac surgery has been shown. Under the steady-state and stable kidney function, SCr is usually produced at a relatively constant rate by the body depending on the absolute amount of muscle mass, and is a reliable and cost-effective surrogate marker for kidney function (33). SCr is strongly correlated with weight, total body water and anthropometrically estimated lean body mass (LBM) (34). Approximately half of LBM is comprised of skeletal muscle mass (35). Recent studies suggest that higher muscle mass is associated with greater longevity in people with CKD and other chronic disease states (36, 37). SCr, however, has several limitations, such as variations in concentration related to age, sex, muscle mass and is influenced by dietary protein intake. (38) Furthermore AKI affects different complex cellular and molecular pathways. Several novel urinary biomarkers such as insulin-like growth factor-binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinases-2 (TIMP-2) and neutral endopeptidase (NEP) are involved in the early phase of cell injury and predict both the development and severity of AKI and renal recovery early after cardiac surgery (39-43) In this study the investigators want to test if increased bSCr is influenced by body composition. Further the investigators want to determine if the incidence of AKI is different in patients below or above the estimated cut-off. Therefore the investigators want to perform a prospective cohort analysis and will take several other body composition and nutrition parameters to test their influence on the predictive power of bSCr. Furthermore the investigators want to evaluate several novel biomarkers for AKI on their predictive effect in cardiac surgical patients.