Measurement of thyroglobulin level in lateral neck lymph node fine needle aspiration washout fluid in papillary thyroid cancer.

Abstract

Thyroglobulin (Tg) level of fine needle aspiration (FNA) washout fluid (FNA-Tg) is useful to detect cervical lymph node (LN) metastasis in patients with papillary thyroid cancer (PTC). The objective of this study was to determine appropriate cutoff values of serum Tg (S-Tg) and FNA-Tg levels for diagnosis of lateral neck LN metastasis and investigate their diagnostic performance. A total of 169 patients with PTC who underwent modified radical neck dissection (mRND) were retrospectively reviewed at Seoul St. Mary's Hospital (Seoul, Korea) from December 2011 to September 2019. Diagnostic performance of FNA-Tg, Tg ratio (FNA-Tg level/S-Tg level), and FNA-Tg combined with Tg ratio was evaluated by correlation with FNA cytology results. FNA-Tg level ≥20 ng/mL exhibited 86.6% sensitivity, 66.7% specificity, and 81.7% accuracy. Tg ratio ≥3 exhibited lower sensitivity but higher specificity (82.7% and 73.8%, respectively) than FNA-Tg level ≥20 ng/mL. FNA-Tg level ≥20 ng/mL combined with Tg ratio ≥3 had 81.9% sensitivity, 80.5% accuracy, and an integrated area under the curve (iAUC) of 0.790. Measurement of FNA-Tg level increases preoperative diagnostic accuracy for the detection of metastatic LNs in patients with PTC. Diagnostic accuracy is higher using a 20 ng/mL FNA-Tg cutoff level. Tg ratio is also valuable and FNA-Tg combined with Tg ratio shows promise.