Clinical Implications of Lymph Node Thyroglobulin in Papillary Thyroid Carcinoma Metastases: Independent from Thyroglobulin Antibody Interference.

Papillary thyroid carcinoma (PTC) frequently involves cervical lymph node (LN) metastases and is a major determinant of prognosis and recurrence. However, cytology alone has limitations. Fine-needle aspiration thyroglobulin (FNA-Tg) has emerged as a promising diagnostic marker, although its cutoff value remains controversial, particularly in patients with thyroglobulin antibodies (TgAbs). We retrospectively analyzed 63 LNs of 60 patients with PTC at a single medical center. Patients underwent FNA-Tg measurements and concurrent cytological evaluation. Diagnostic performance metrics, including sensitivity, specificity, positive and negative predictive value, and overall accuracy, were evaluated; the cutoff value was determined; and the potential influence of factors such as TgAb on FNA-Tg levels was investigated. A cutoff value of 4.23 ng/mL for FNA-Tg achieved 100% sensitivity and 90.2% specificity, with an overall accuracy of 93.6%. TgAb positivity did not significantly affect the diagnostic performance in patients with FNA-Tg. FNA-Tg might be useful for detecting local LN recurrence and providing valuable diagnostic insights, particularly in patients with residual thyroid tissue or positive TgAbs.