Chionh Chang Yin, Tien Carolyn Shan-Yeu, Yeon Wenxiang
Department of Renal Medicine, Changi General Hospital, Singapore.
Renal Medicine, SingHealth Residency, Singapore.
Singapore Med J. 2024 Mar 13. doi: 10.4103/singaporemedj.SMJ-2023-009.
The anion gap (AG) is commonly used to screen for acid-base disorders. It was proposed that the cut-off for high anion gap metabolic acidosis (HAGMA) may be lower with current laboratory techniques, although modern laboratory equipment are still calibrated to familiar reference ranges established with earlier techniques. The appropriate cut-off for HAGMA is unclear. This study aimed to assess the performance of AG as a screening test for HAGMA and to determine the optimal diagnostic threshold of AG for HAGMA.
This was a retrospective analysis of a large, anonymised dataset extracted by computerised protocol from 2017 to 2019. All inpatients with blood samples taken for organic acids (lactate, ketone or salicylate) paired with a metabolic panel were included. The target condition was HAGMA secondary to elevated blood lactate, ketone and/or salicylate. Sensitivity for HAGMA was explored at various AG cut-off levels.
Of 16,475 patients, 2,621 had organic acidosis. Median age was 65 years, and median estimated glomerular filtration rate was 70 mL/min/1.73 m2. With organic acidosis, the median AG was 23 (interquartile range [IQR] 20-29) mEq/L, while without organic acidosis, the median AG was 16 (IQR 14-19) mEq/L. The area under the curve-receiver operating characteristic of AG for HAGMA was 0.873. Desired sensitivity for HAGMA was set at ≥95%, and this was found with an AG threshold of ≥15 mEq/L (sensitivity 98.1%, specificity 34.0%).
The recommended AG threshold value is ≥15 mEq/L with a high sensitivity for HAGMA. The AG should always be interpreted with the clinical context, and it should be repeated as the clinical picture evolves.
阴离子间隙（AG）常用于筛查酸碱紊乱。有人提出，鉴于当前实验室技术，高阴离子间隙代谢性酸中毒（HAGMA）的临界值可能较低，尽管现代实验室设备仍按照早期技术确定的熟悉参考范围进行校准。HAGMA的合适临界值尚不清楚。本研究旨在评估AG作为HAGMA筛查试验的性能，并确定HAGMA的AG最佳诊断阈值。
这是一项对2017年至2019年通过计算机程序提取的大型匿名数据集进行的回顾性分析。纳入所有采集了有机酸（乳酸、酮体或水杨酸盐）血样并同时进行代谢指标检测的住院患者。目标疾病为继发于血乳酸、酮体和/或水杨酸盐升高的HAGMA。在不同的AG临界值水平下探讨HAGMA的敏感性。
16475例患者中，2621例存在有机酸血症。中位年龄为65岁，中位估计肾小球滤过率为70 mL/min/1.73 m²。发生有机酸血症时，AG的中位数为23（四分位间距[IQR]20 - 29）mEq/L，未发生有机酸血症时，AG的中位数为16（IQR 14 - 19）mEq/L。AG用于HAGMA的曲线下面积-受试者工作特征曲线为0.873。将HAGMA的期望敏感性设定为≥95%，发现AG阈值≥15 mEq/L时可达到该敏感性（敏感性98.1%，特异性34.0%）。
推荐的AG阈值为≥15 mEq/L，对HAGMA具有高敏感性。AG应始终结合临床情况进行解读，并且应随着临床病情的演变重复检测。
