BACKGROUND-AIM Measurement of serum thyrotropin is currently the recommended test for the screening of thyroid dysfunction, while serum free thyroxine is kept as a reflex test. In our laboratory, the strategy followed in adult individuals from Primary Care includes a 'safety margin' for requests with a thyrotropin ≤1.0 or ≥4.0 mIU/L (normal: 0.35-4.95 mIU/L). Our aim was to optimize the thyrotropin cut-off values for the addition of free thyroxine and, based on these cut-offs, to retrospectively analyze avoidable free thyroxine measurements and possible adverse clinical consequences. METHODS Retrospective observational study performed in a tertiary care hospital between 2013 and 2018. We considered all laboratory requests for screening of thyroid dysfunction (TD) in adult patients from Primary Care. Requests from patients with a previous diagnosis of thyroid disease or pregnant women were excluded. Different receiver operating characteristic (ROC) curves were performed and the obtained thyrotropin cut-off values were compared. Economic savings were assessed considering the current cost of free thyroxin assays in our laboratory. RESULTS From a total of 554,529 TD protocols included, 119,504 requests had free thyroxine added. From the ROC curve that enables ≥95% of abnormal free thyroxine results to be detected, the thyrotropin values obtained were ≥4.58 mIU/L and ≤0.94 mIU/L. These thyrotropin cut-off values would lead to a saving of 22.7% of annual free thyroxine measurements without adverse clinical consequences. DISCUSSION Setting optimized thyrotropin cutoffs for reflex testing of free thyroxine would reduce the need for this test. Clinical laboratories need to offer not only true results, but also become the cornerstone in the optimization of resources.

中文翻译：

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用于诊断目的的甲状腺组优化：反射性添加游离甲状腺素的促甲状腺激素截止值。

背景-目的 血清促甲状腺素的测量目前是筛查甲状腺功能障碍的推荐测试，而血清游离甲状腺素作为反射测试保留。在我们的实验室中，初级保健成人个体所遵循的策略包括对促甲状腺素≤1.0 或 ≥4.0 mIU/L（正常：0.35-4.95 mIU/L）的请求的“安全范围”。我们的目标是优化添加游离甲状腺素的促甲状腺激素临界值，并基于这些临界值，回顾性分析可避免的游离甲状腺素测量值和可能的不良临床后果。方法 2013 年至 2018 年在一家三级护理医院进行的回顾性观察研究。我们考虑了所有实验室对初级保健成人患者甲状腺功能障碍 (TD) 筛查的要求。先前诊断为甲状腺疾病的患者或孕妇的请求被排除在外。进行了不同的受试者工作特征（ROC）曲线，并比较了获得的促甲状腺激素截止值。考虑到我们实验室目前免费甲状腺素检测的成本，评估了经济节约。结果 在总共包含的 554,529 个 TD 协议中，119,504 个请求添加了游离甲状腺素。从能够检测到≥95%的异常游离甲状腺素结果的ROC曲线来看，获得的促甲状腺素值分别为≥4.58 mIU/L和≤0.94 mIU/L。这些促甲状腺激素临界值将导致每年节省 22.7% 的游离甲状腺素测量值，而不会产生不利的临床后果。讨论 为游离甲状腺素的反射测试设置优化的促甲状腺激素截止值将减少对该测试的需求。