Detection of thyroglobulin for diagnosis of metastatic lateral cervical lymph nodes in papillary thyroid carcinoma: accuracy and application in clinical practice.

Background: Accurate assessment of lateral cervical lymph node metastasis (LLNM) involvement is important for treating papillary thyroid carcinoma (PTC). Thyroglobulin is associated with LLNM, but there may be differences in the diagnostic value of serum thyroglobulin (sTg) and fine needle aspiration washout fluid thyroglobulin (FNA-Tg). Herein, we investigated the optimal cutoff value (OCV) of sTg and FNA-Tg and their diagnostic performance. Methods: We enrolled 116 PTC patients who underwent radical resection of thyroid carcinoma with lateral cervical lymph node dissection at the Affiliated Hospital of Zunyi Medical University from June 2018 to July 2022. We used the receiver operating characteristic (ROC) curve analysis to determine the OCV for sTg and FNA-Tg to diagnose LLNM in PTC patients. We also evaluated the performance of FNA-Tg, sTg, fine needle aspiration cytology (FNAC), and their combinations for diagnosis. Pathological results were the gold standard. Results: We performed 125 lymph node dissections, 106 had metastasis, and 19 did not. The OCV for sTg was 17.31 ng/mL [area under the curve (AUC) =0.760, sensitivity =78.30%, specificity =73.68%, and accuracy =77.60%]. Meanwhile, the OCV for FNA-Tg was 4.565 ng/mL (AUC =0.948, sensitivity =89.62%, specificity =100%, and accuracy =91.20%). The combination of FNAC and FNA-Tg presented the greatest diagnostic performance for LLNM detection in PTC patients. Moreover, serum antithyroglobulin antibody (TgAb) was not correlated with sTg or FNA-Tg levels. Conclusions: The cutoff value for the diagnosis of LLNM in PTC are sTg >17.31 ng/mL or FNA-Tg >4.565 ng/mL. The combination method of FNA-Tg and FNAC is the most optimal choice for the diagnosis of LLNM and is highly recommended for further clinical application.