Purpose: Most blunt renal injuries (BRIs) are managed conservatively without complications. Because conservative management with observation (CMO) is widely conducted, failed CMO is frequent. Clarifying the role and indication of CMO is important to manage BRI patients. Therefore, this study was conducted to analyse factors related to failed CMO. Methods: BRI patients (aged > 13 years) who were admitted via the emergency department in Wonju Severance Christian Hospital were analysed retrospectively between January 2008 and July 2020. Patient characteristics, including clinical data, laboratory findings, transfusion requirements, injury grade, initial CT findings, length of hospital stay, intensive care unit stay, and mortality, were investigated for all enrolled patients. Results: Kidney injury grade >= 4, perinephric haematoma rim distance (PHD), length of main laceration, intravascular contrast extravasation (ICE), Gerota's fascia discontinuity, multiple lacerations, dissociated renal fragment and complexity of laceration were statistically significantly different between the successful CMO and failed CMO groups in the comparative analysis. The multivariate analysis showed that perinephric haematoma rim distance [odds ratio (OR) 1.44 [95% confidence interval (CI) 1.09 - 1.90], p = 0.011] and ICE [OR 7.41 (95% CI 2.20 - 24.99), p = 0.001] were mutually independent risk factors associated with failed CMO. When the ROC curve of PHD and ICE was generated to predict the failure of CMO, the area under the curve (AUC) was 0.884 (95% CI, 0.826 - 0.942), p < 0.001), and the optimal cut-off value for PHD was 2.9 cm, and for ICE was presence of ICE on CT [sensitivity: 90.5% (95% CI, 0.70 - 0.99), specificity: 78.0% (95% CI, 0.73 - 0.83)]. Conclusion: PHD and ICE may be useful factors to predict failed CMO for BRI patients. PHD > 2.9 cm and the presence of ICE may indicate who will require invasive procedures. Close observation is wise for patients with these risk factors. (C) 2021 The Authors. Published by Elsevier Ltd.
