Background Twenty-four-hour urinary free cortisol (UFC) measurement is the initial diagnostic test for Cushing's syndrome (CS). We compared UFC determination by both direct and extraction immunoassays using Abbott Architect, Siemens Atellica Solution, and Beckman DxI800 with liquid chromatography-tandem mass spectrometry (LC-MS/MS). In addition, we evaluated the value of 24-hr UFC measured by six methods for diagnosing CS. Methods Residual 24-hr urine samples of 94 CS and 246 non-CS patients were collected. A laboratory-developed LC-MS/MS method was used as reference. UFC was measured by direct assays (D) using Abbott, Siemens, and Beckman platforms and by extraction assays (E) using Siemens and Beckman platforms. Method was compared using Passing-Bablok regression and Bland-Altman plot analyses. Cut-off values for the six assays and corresponding sensitivities and specificities were calculated by ROC analysis. Results Abbott-D, Beckman-E, Siemens-E, and Siemens-D showed strong correlations with LC-MS/MS (Spearman coefficient r=0.965, 0.922, 0.922, and 0.897, respectively), while Beckman-D showed weaker correlation (r=0.755). All immunoassays showed proportionally positive bias. The areas under the curve were 0.975 for Abbott-D, 0.972 for LC-MS/MS, 0.966 for Siemens-E, 0.948 for Siemens-D, 0.955 for Beckman-E, and 0.877 for Beckman-D. The cut-off values varied significantly (154.8-1,321.5 nmol/24 hrs). Assay sensitivity and specificity ranged from 76.1% to 93.2% and from 93.0% to 97.1%, respectively. Conclusions Commercially available immunoassays for measuring UFC show different levels of analytical consistency compared to LC-MS/MS. Abbott-D, Siemens-E, and Beckman-E have high diagnostic accuracy for CS.

中文翻译：

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直接和提取免疫测定方法与液相色谱-串联质谱测量尿游离皮质醇诊断库欣综合征的比较。

背景 24 小时尿游离皮质醇 (UFC) 测量是库欣综合征 (CS) 的初步诊断测试。我们将使用 Abbott Architect、Siemens Atellica Solution 和 Beckman DxI800 的直接免疫测定法和提取免疫测定法与液相色谱-串联质谱法 (LC-MS/MS) 进行的 UFC 测定进行了比较。此外，我们评估了通过六种方法测量的 24 小时 UFC 的诊断 CS 的价值。方法收集94例CS患者和246例非CS患者的24小时残余尿样。使用实验室开发的 LC-MS/MS 方法作为参考。UFC 通过使用 Abbott、Siemens 和 Beckman 平台的直接测定法 (D) 以及使用西门子和 Beckman 平台的提取测定法 (E) 进行测量。使用 Passing-Bablok 回归和 Bland-Altman 图分析对方法进行比较。通过 ROC 分析计算六种测定的截止值以及相应的敏感性和特异性。结果 Abbott-D、Beckman-E、Siemens-E、Siemens-D 与 LC-MS/MS 的相关性较强（Spearman 系数 r 分别为 0.965、0.922、0.922、0.897），Beckman-D 的相关性较弱（r=0.755）。所有免疫测定均显示出成比例的阳性偏倚。曲线下面积为 Abbott-D 0.975、LC-MS/MS 0.972、Siemens-E 0.966、Siemens-D 0.948、Beckman-E 0.955 和 Beckman-D 0.877。截止值差异很大（154.8-1,321.5 nmol/24 小时）。检测灵敏度和特异性范围分别为 76.1% 至 93.2% 和 93.0% 至 97.1%。结论 与 LC-MS/MS 相比，市售的 UFC 免疫测定法显示出不同程度的分析一致性。Abbott-D、Siemens-E 和 Beckman-E 对 CS 的诊断准确性较高。