Supplementary Material for: The impact of C-reactive protein-to-albumin ratio on mortality in patients with acute kidney injury requiring continuous renal replacement therapy: A multicenter retrospective study

Introduction: C-reactive protein-to-albumin ratio (CAR) is a prognostic marker in various diseases that represents patients’ inflammation and nutritional status. Here, we aimed to investigate the prognostic value of CAR in critically ill patients with severe acute kidney injury (AKI) requiring continuous renal replacement therapy (CRRT). Methods: We retrospectively collected data from eight tertiary hospitals in Korea from 2006–2021. The patients were divided into quartiles according to CAR levels at the time of CRRT initiation. Cox regression analyses were performed to investigate the effect of CAR on in-hospital mortality. The mortality prediction performance of CAR was evaluated using the area under the curve (AUC), net reclassification improvement (NRI), and integrated discrimination improvement (IDI). Results: In total, 3995 patients who underwent CRRT were included, and the in-hospital mortality rate was 67.3% during the follow-up period. The 7-day, 30-day, and in-hospital mortality rates increased toward higher CAR quartiles (all P < 0.001). After adjusting for confounding variables, the higher quartile groups had an increased risk of in-hospital mortality (quartile 3: adjusted hazard ratio [aHR], 1.26, 95% confidence interval [CI], 1.10–1.43, P < 0.001; quartile 4: aHR, 1.22, 95% CI, 1.07–1.40, P = 0.003). CAR combined with APACHE II or SOFA scores significantly increased the predictive power compared to each severity score alone for the AUC, NRI, and IDI (all P < 0.05). Conclusions: A high CAR is associated with increased in-hospital mortality in critically ill patients requiring CRRT. The combined use of CAR and severity scores provides better predictive performance for mortality than the severity score alone.

引言：C反应蛋白与白蛋白比值（C-reactive protein-to-albumin ratio, CAR）是多种疾病的预后标志物，可反映患者的炎症状态与营养状况。本研究旨在探讨CAR在需接受连续性肾脏替代治疗（continuous renal replacement therapy, CRRT）的重症急性肾损伤（severe acute kidney injury, AKI）危重患者中的预后价值。
方法：本研究回顾性收集了2006年至2021年韩国8家三级医院的临床数据。根据患者启动CRRT时的CAR水平将其分为四等分组。采用Cox回归分析探讨CAR对患者住院死亡率的影响。通过曲线下面积（area under the curve, AUC）、净重新分类指数（net reclassification improvement, NRI）及综合判别改善指数（integrated discrimination improvement, IDI）评估CAR的死亡率预测效能。
结果：本研究共纳入3995例接受CRRT的患者，随访期间住院死亡率为67.3%。随着CAR四分位组升高，7天、30天及住院死亡率均呈上升趋势（所有P<0.001）。校正混杂变量后，较高四分位组的住院死亡风险显著升高（第3四分位组：校正后风险比（adjusted hazard ratio, aHR）=1.26，95%置信区间（confidence interval, CI）=1.10~1.43，P<0.001；第4四分位组：aHR=1.22，95%CI=1.07~1.40，P=0.003）。与单独使用单一严重程度评分相比，CAR联合APACHE II或SOFA评分可显著提升死亡率预测效能，体现在AUC、NRI及IDI方面（所有P<0.05）。
结论：高CAR水平与需接受CRRT的危重患者住院死亡风险升高显著相关。联合使用CAR与严重程度评分，其死亡率预测效能优于单独使用单一严重程度评分。