Background/Objectives: Patients with differentiated thyroid cancer (DTC) receive thyroxine substitution targeting thyroid-stimulating hormone (TSH) levels based on their treatment response category. However, variations in prescribing and inter-assay TSH variability may result in over or undertreatment. Methods: We measured TSH in 220 consecutive DTC patients using three automated immunoassay platforms (Elecsys, Atellica, Alinity). Each patient was assigned to a response-to-therapy category (Excellent Response [ER], Indeterminate Response [IndR], Biochemical Incomplete Response [BIR], Structural Incomplete Response [SIR]) by an experienced thyroid oncologist. We defined recommended TSH targets according to the American Thyroid Association (ATA) 2015 guidelines and the response-adapted ATA 2025 framework that allows progressive relaxation of TSH suppression in patients with ER while maintaining tight suppression in those with persistent disease. Analytical agreement between assays was assessed using Passing–Bablok regression and Bland–Altman analysis. Clinical appropriateness was evaluated by classifying each measured TSH value as below, within, or above the recommended range for that patient’s response category. Results: The three immunoassays demonstrated high analytical agreement with only minor biases unlikely to affect clinical interpretation. However, significant deviations from guideline-defined TSH targets were observed. Among ER patients, 37% remained oversuppressed despite the absence of active disease. Conversely, in IndR or BIR patients, 76% had TSH levels above the recommended range, indicating undersuppression where residual disease could not be excluded. SIR patients were generally managed appropriately. The ATA 2025 framework reclassified more ER patients as appropriately managed, but undersuppression persisted in non-ER patients. Conclusions: Guidelines are not uniformly applied in thyroxine dosing for DTC patients. TSH immunoassays have achieved adequate analytical performance. The focus must now shift toward addressing clinical, educational, and systemic factors that prevent optimal levothyroxine management.
背景/目的：分化型甲状腺癌（DTC）患者接受左甲状腺素替代治疗，其促甲状腺激素（TSH）水平目标值基于治疗反应类别设定。然而，处方差异及不同检测方法间的TSH变异可能导致治疗过度或不足。方法：我们使用三种自动化免疫检测平台（Elecsys、Atellica、Alinity）连续测量了220例DTC患者的TSH水平。每位患者均由经验丰富的甲状腺肿瘤学家根据治疗反应类别进行评估分类（疗效优异[ER]、疗效不确定[IndR]、生化反应不完全[BIR]、结构反应不完全[SIR]）。我们依据美国甲状腺协会（ATA）2015年指南及反应适应性ATA 2025框架设定了推荐TSH目标值，该框架允许对ER患者逐步放宽TSH抑制，而对存在持续病灶的患者维持严格抑制。采用Passing–Bablok回归和Bland–Altman分析评估检测方法间的一致性。通过将每个实测TSH值与该患者反应类别的推荐范围进行比较（低于、在范围内或高于），评估临床管理的适宜性。结果：三种免疫检测方法显示出高度的一致性，仅存在微小偏差，不太可能影响临床判读。然而，观察到与指南定义的TSH目标值存在显著偏离。在ER患者中，37%仍处于过度抑制状态，尽管无活动性疾病。相反，在IndR或BIR患者中，76%的TSH水平高于推荐范围，表明存在抑制不足，且不能排除残留病灶。SIR患者的管理总体适当。ATA 2025框架将更多ER患者重新归类为管理适当，但非ER患者的抑制不足问题持续存在。结论：DTC患者的左甲状腺素剂量管理中，指南未得到统一应用。TSH免疫检测已达到足够的分析性能。当前重点必须转向解决阻碍左甲状腺素优化管理的临床、教育和系统性因素。
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