Diagnostic value of thyroglobulin washout in fine-needle aspiration samples for diagnosis and follow-up of differentiated thyroid cancer

Our goal was to assess the effectiveness of fine-needle aspiration thyroglobulin (FNA-Tg) in detecting malignant lymph nodes (LNs) in patients with differentiated thyroid cancer (DTC). We also aimed to determine the factors that affect the accuracy of FNA-Tg. We conducted a retrospective cohort study using the laboratory, ultrasonographic, histopathological, FNA cytology (FNA-C), and FNA-Tg results of 176 DTC patients. We used receiver operating characteristic analysis to identify the cutoff value of FNA-Tg, and binary regression analysis to compare FNA-Tg with other diagnostic parameters. Spearman correlation was utilized to identify factors that influence FNA-Tg. Our study revealed that a cutoff value of 3.14 ng/mL for FNA-Tg had a sensitivity of 91.8% and a specificity of 96.6% in detecting malignant LNs in the entire group. In the subgroup with thyroid tissue, the optimal cutoff value for FNA-Tg was determined to be 15.5 ng/mL. Additionally, FNA-C had a sensitivity of 82.4% and a specificity of 99.4% for the entire group. The combined use of FNA-Tg and FNA-C yielded a sensitivity of 100% and a specificity of 96%, which was found to be more effective than using either test alone. Serum Tg positivity and serum thyroid-stimulating hormone were positively correlated with FNA-Tg levels in detecting malignant LNs. Our study demonstrated that FNA-Tg is a reliable method for detecting LN metastases in DTC patients, with a 3.14 ng/mL cutoff value. However, each center should take into account factors such as serum thyroid-stimulating hormone, serum Tg, and the presence of thyroid tissue when interpreting FNA-Tg results and determining the appropriate cutoff level.