Background: Thyroglobulin (Tg) assay in washout fluids of fine needles, after cervical lymph nodes aspiration, is used for detecting metastases from differentiated thyroid carcinomas. Assay methods are the same as for Tg in serum. However, with non-serum samples, methods require extensive validation to notably check for the absence of matrix effect. This study fits this context. Our objectives were to assess analytic performances, in washout fluid, of 8 different Tg assay methods and to compare them to validated data in serum.

Methods: Eleven medical laboratories participated in this study. The matrix tested was phosphate-buffer saline containing 1 % bovine serum albumin (PBS-1% BSA). Samples used were dilutions, in this buffer, of Certified Reference Material (CRM 457). We verified, for all methods, the limit of detection, precision, linearity, trueness and accuracy.

Results: In PBS-1% BSA, the functional sensitivities (FS) were comparable to those expected for serum. All the methods were linear. The relative biases of trueness were between -24.5 and 10.2 % around 1 µg/L. Total analytical error was ≤ 40 % near the FS values.

Conclusion: No quantitatively important matrix effect was observed. All the methods showed their ability to measure Tg in PBS-1% BSA, over the concentration range of interest, with acceptable total analytical error. We validated the FS value as a decision threshold in thyroidectomized patients after treatment and with low levels of serum Tg.

背景：在抽吸颈部淋巴结后，细针冲洗液中的甲状腺球蛋白（Tg）测定可用于检测分化的甲状腺癌的转移。测定方法与血清中Tg的测定方法相同。但是，对于非血清样品，方法需要进行大量验证，以特别检查是否存在基质效应。这项研究适合这种情况。我们的目标是评估8种不同Tg分析方法在冲洗液中的分析性能，并将其与血清中的验证数据进行比较。

方法：11个医学实验室参加了这项研究。测试的基质是含有1％牛血清白蛋白（PBS-1％BSA）的磷酸盐缓冲盐水。使用的样品是在该缓冲液中稀释的标准参考物质（CRM 457）。我们验证了所有方法的检测极限，精确度，线性，真实性和准确性。

结果：在PBS-1％BSA中，功能敏感性（FS）与预期的血清相当。所有方法都是线性的。真实性的相对偏差在-24.5和10.2％之间，大约1 µg / L。FS值附近的总分析误差约为40％。

结论：未观察到定量上重要的基质效应。所有方法均显示了它们在感兴趣的浓度范围内测量PBS-1％BSA中Tg的能力，并且具有可接受的总分析误差。我们验证了FS值作为治疗后甲状腺切除术且血清Tg水平低的患者的决策阈值。