Abstract: Objective To assess the clinical value of CT severity index (CTSI) combined with lactate in predicting acute kidney injury (AKI) in elderly patients with severe acute pancreatitis (SAP)during hospitalization. 
Methods A total of 328 elderly SAP patients hospitalized in the First Hospital of Harbin Medical University were retrospectively included, and were divided into the AKI group (n=68, 20.73%)and the non-AKI group (n=260, 79.07%) according to whether AKI occurred during hospitalization. The clinical data of all patients were collected through the inpatient medical record system. Multivariate Logistic regression analysis was used to screen the risk factors for AKI during hospitalization in SAP patients, and receiver operating characteristic (ROC) curve was used to assess the clinical efficacy of CTSI and lactate in predicting the occurrence of AKI. 
Results Univariate analysis showed that age ＞70 years, diabetes mellitus, morbidity and mortality, proportion of consecutive renal replacement therapy, and interleukin 6, lactate, CTSI, sequential organ failure estimation score, acute physiology and chronic health evaluation Ⅱ scores, and Charlson comorbidity index were higher in AKI group than in the non-AKI group, showing significant difference (P＜0.05). The results of multivariate Logistic regression analysis showed that age ＞70 years (OR=1.267, 95%CI: 1.042-1.541), CTSI (OR=1.632, 95%CI: 1.291-2.064), and lactate (OR=1.428, 95%CI: 1.133-1.798) were risk factors for AKI in SAP patients during hospitalization. The ROC curve showed that the area under the ROC curve (AUC) of CTSI combined with lactate in patients with SAP complicated with AKI was ［0.869 (95%CI: 0.818-0.920)］, which was higher than that predicted by CTSI ［0.733 (95%CI: 0.664-0.802)］, and orlactate ［0.695 (95%CI: 0.624-0.766)］ alone, showing optimal predictive performance. 
Conclusion CTSI and lactate are independent risk factors for AKI during hospitalization in SAP patients, and the combined detection can predict the risk of AKI, and then assist in clinical practice to screen out the high-risk group for targeted intervention. 

Key words: pancreatitis, acute kidney injury, CT severity index, lactate