The current definition of acute kidney injury (AKI) includes increased serum creatinine (sCr) concentration and decreased urinary output (UO). Recent studies suggest that the standard UO threshold of 0.5 ml/kg/h may be suboptimal. This study aimed to develop and validate a novel UO-based AKI classification system that improves mortality prediction and patient stratification. Data were obtained from the MIMIC-IV and eICU databases. The development process included (1) evaluating UO as a continuous variable over 3-, 6-, 12-, and 24-h periods; (2) identifying 3 optimal UO cutoff points for each time window (stages 1, 2, and 3); (3) comparing sensitivity and specificity to develop a unified staging system; (4) assessing average versus persistent reduced UO hourly; (5) comparing the new UO-AKI system to the KDIGO UO-AKI system; (6) integrating sCr criteria with both systems and comparing them; and (7) validating the new classification with an independent cohort. In all these steps, the outcome was hospital mortality. Another analyzed outcome was 90-day mortality. The analyses included ROC curve analysis, net reclassification improvement (NRI), integrated discrimination improvement (IDI), and logistic and Cox regression analyses. From the MIMIC-IV database, 35,845 patients were included in the development cohort. After comparing the sensitivity and specificity of 12 different lowest UO thresholds across four time frames, 3 cutoff points were selected to compose the proposed UO-AKI classification: stage 1 (0.2–0.3 mL/kg/h), stage 2 (0.1–0.2 mL/kg/h), and stage 3 (< 0.1 mL/kg/h) over 6 h. The proposed classification had better discrimination when the average was used than when the persistent method was used. The adjusted odds ratio demonstrated a significant stepwise increase in hospital mortality with advancing UO-AKI stage. The proposed classification combined or not with the sCr criterion outperformed the KDIGO criteria in terms of predictive accuracy—AUC-ROC 0.75 (0.74–0.76) vs. 0.69 (0.68–0.70); NRI: 25.4% (95% CI: 23.3–27.6); and IDI: 4.0% (95% CI: 3.6–4.5). External validation with the eICU database confirmed the superior performance of the new classification system. The proposed UO-AKI classification enhances mortality prediction and patient stratification in critically ill patients, offering a more accurate and practical approach than the current KDIGO criteria.

中文翻译：

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重新定义危重患者急性肾损伤标准的尿量阈值：推导和验证研究


目前急性肾损伤（AKI）的定义包括血清肌酐（sCr）浓度升高和尿量（UO）减少。最近的研究表明，0.5 ml/kg/h 的标准 UO 阈值可能不是最理想的。本研究旨在开发和验证一种基于 UO 的新型 AKI 分类系统，该系统可改善死亡率预测和患者分层。数据来自 MIMIC-IV 和 eICU 数据库。开发过程包括 (1) 将 UO 作为 3、6、12 和 24 小时周期内的连续变量进行评估； (2) 确定每个时间窗口的 3 个最佳 UO 截止点（阶段 1、2 和 3）； (3)比较敏感性和特异性，制定统一的分期系统； (4) 评估平均每小时 UO 与持续减少的 UO； (5)将新的UO-AKI系统与KDIGO UO-AKI系统进行比较； (6) 将 sCr 标准与两个系统相结合并进行比较； (7) 通过独立队列验证新分类。所有这些步骤的结果都是医院死亡率。另一个分析结果是 90 天死亡率。分析包括 ROC 曲线分析、净重分类改进 (NRI)、综合辨别改进 (IDI) 以及逻辑回归和 Cox 回归分析。 MIMIC-IV 数据库中，开发队列中纳入了 35,845 名患者。在比较了四个时间范围内 12 个不同的最低 UO 阈值的敏感性和特异性后，选择了 3 个截止点来组成拟议的 UO-AKI 分类：第 1 阶段（0.2–0.3 mL/kg/h）、第 2 阶段（0.1–0.2 mL/kg/h)，以及 6 小时内的第 3 阶段 (< 0.1 mL/kg/h)。使用平均值时所提出的分类比使用持久方法时具有更好的区分度。 调整后的比值比表明，随着 UO-AKI 分期的进展，医院死亡率显着逐步增加。所提出的分类无论是否与 sCr 标准结合使用，在预测准确性方面均优于 KDIGO 标准 — AUC-ROC 0.75 (0.74–0.76) vs. 0.69 (0.68–0.70)； NRI：25.4%（95% CI：23.3–27.6）； IDI：4.0%（95% CI：3.6–4.5）。 eICU 数据库的外部验证证实了新分类系统的卓越性能。拟议的 UO-AKI 分类增强了危重患者的死亡率预测和患者分层，提供了比当前 KDIGO 标准更准确、更实用的方法。