Optimal cutoff value of fine-needle aspiration thyroglobulin of metastatic lymph node in thyroid cancer patients.

[OBJECTIVE] Thyroglobulin in fine-needle aspiration washout fluids (FNA-Tg) has been recognized as a valuable tool for detecting lymph node metastases (LNM) in papillary thyroid carcinoma (PTC). However, the optimal cutoff value for FNA-Tg remains unclear. We analyzed interference of factors such as serum Tg, serum TgAb on FNA-Tg, and determined the optimal cutoff value of FNA-Tg.

[SUBJECTS] and methods: We conducted a retrospective analysis of patients diagnosed as PTC with suspicious cervical lymph node between August 2015 and May 2023. Fine-needle aspiration (FNA) and FNA-Tg measurement were performed on suspicious lateral cervical lymph nodes. Final diagnose was determined by FNA cytology (FNAC) or histopathological examination. For FNAC negative lymph node, patients received follow-up for at least 1year.

[RESULTS] A total of 10,503 lateral cervical lymph nodes from 4259 patients were included in the study, with 2583 lymph nodes identified as metastatic. Receiver operating characteristic (ROC) curve analysis determined the optimal cutoff value for FNA-Tg to be 0.865 ng/mL for all patients, with a sensitivity of 80.0 % and specificity of 94.4 % respectively. When combining with FNAC and thyroglobulin ratio assessment, it achieved an overall diagnostic accuracy of 96.6 %. FNA-Tg was correlated with serum Tg and thyroid gland status (p<0.001), and no significant correlation was observed between FNA-Tg and serum TgAb (P = 0.66) or TSH (P = 0.31).

[CONCLUSION] FNA-Tg demonstrates high accuracy in the diagnosis of metastatic lymph nodes, and the optimal cutoff value is related with serum Tg and thyroid glands status.