BACKGROUND: The aim of this study was to develop a simple risk score to estimate severe acute kidney injury (AKI) risk based on a large contemporary heart transplantation (HT) cohort. METHODS: From 1 January 2015 to 31 December 2021, all consecutive HT recipients in our institute were included and analysed for the occurrence of AKI within the first seven postoperative days. Patients transplanted between 2015 and 2019 comprised the derivation cohort, and those transplanted between 2020 and 2021 formed the validation cohort. The primary endpoint was severe AKI (AKI stages 2-3). The impact of severe AKI on 90 day mortality was also evaluated. RESULTS: Overall, 430 HT patients were included in the derivation cohort, and 108 were included in the validation cohort. Postoperative AKI occurred in 388 (72%) patients, including 162 (30%) severe AKI. The risk of 90 day mortality significantly increased in patients with severe-AKI. Seven independent predictors of severe AKI were found in the derivation cohort, including recipients' body mass index, history of diabetes, anaemia, preoperative inotropes, estimated glomerular filtration rate, cardiopulmonary bypass duration and intraoperative red blood cell transfusion. The occurrence of severe AKI increased gradually from the lowest to the highest of the four risk score groups in the derivation and validation cohort. The scoring prediction model showed a highly acceptable discriminating power for severe-AKI [C statistic: 0.76, 95% confidence interval (CI): 0.71-0.80 for derivation cohort
C statistic: 0.79, 95% CI: 0.71-0.89 for validation cohort]. CONCLUSIONS: A contemporary simple risk score based on available variables from patients undergoing HT can accurately discriminate the risk of severe AKI.