The Predictive Value of the Oxford Acute Disease Severity Score for Clinical Outcomes in Patients with Acute Kidney Injury: A Secondary Analysis of a Large Prospective Observational Study

Abstract Background: To compare the performance of the Oxford Acute Severity of Illness Score (OASIS), the Acute Physiology and Chronic Health Evaluation II (APACHE II) score, the Simplified Acute Physiology Score II (SAPS II) and the Sequential Organ Failure Assessment (SOFA) score in predicting 28-day mortality in acute kidney injury (AKI) patients.Methods: Data were extracted from the Beijing Acute Kidney Injury Trial (BAKIT). 2,954 patients with complete clinical data were included in this study. We calculated the OASIS, APACHE II, SAPS II and SOFA within the first day of ICU admission. Receiver operating characteristic (ROC) curves were used to analyse and evaluate the predictive effects of the four scoring systems on the 28-day mortality risk of AKI patients and each subgroup. The best cut-off value was identified by the highest combined sensitivity and specificity using Youden’s index. The significance level was set at 5%.Results: Among the 2,954 patients, the 28-day mortality rate was 17.0% (501 patients died). The OASIS, APACHE II, SAPS II and SOFA of nonsurviving patients were higher than those of surviving patients with AKI. The 28-day mortality of AKI patients increased accordingly with the increase in OASIS. Among the four scoring systems, the area under the curve (AUC) of OASIS was the highest. The comparison of AUC values of different scoring systems showed that there were no significant differences among OASIS, APACHE II and SAPS II, which were better than SOFA. Moreover, logistic analysis revealed that OASIS was an independent risk factor for 28-day mortality in AKI patients, whether as a continuous variable or a categorical variable. OASIS also had good performance in predicting ICU mortality and in-hospital mortality in AKI patients and had good predictive ability for the 28-day mortality of each subgroup of AKI patients.Conclusion: OASIS, APACHE II and SAPS II all presented good discrimination and calibration in predicting the 28-day mortality risk of AKI patients. OASIS, APACHE II and SAPS II had better predictive accuracy than SOFA, but due to the complexity of APACHE II and SAPS II calculations, OASIS is a good substitute.Trial RegistrationThis study was registered at www.chictr.org.cn (registration number Chi CTR-ONC-11001875). Registered on 14 December 2011.