Thyroglobulin in lymph node fine-needle aspiration biopsy washout fluid. A tertiary center experience

Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer. Most PTC secretes thyroglobulin, a useful marker in monitoring preoperative staging and postoperative progression; in addition to serum thyroglobulin, fine needle aspiration washout thyroglobulin (FNA-Tg) is also used. Our aim was to determine the cut-off value for FNA-Tg in our center and to describe major discrepancies between FNA-Tg, cytology and pathology results of the lymph nodes. Methods: We retrospectively retrieved from the electronic database of our endocrinology center all the FNA-Tg measurements between December 10, 2019 and September 2021. For each measurement we also retrieved the corresponding sex, FNAB results and the pathology reports. FNA-Tg was measured by ECLIA immunoelectro-chemiluminescent method. Results: There were 58 FNAB and FNA-Tg of suspect cervical lymph nodes in 40 patients. There were 17 cytologically benign lymph nodes of which 13 had low and 4 had high FNA-Tg; 3 non-diagnostic cytology results of which one had high FNA-Tg; 38 PTC metastases of which 6 had low and 32 had high FNA-Tg titers. The cut-off value of FNA-Tg in our center is 10 ng/ml, with a sensitivity of 86.6% (in those with pathology reports available after surgery). Conclusions: Washout TG is useful in suspicious lymph nodes and has added value to cytology in selected cases. The cut-off value of FNA-Tg in our center is 10 ng/ml, with a sensitivity of 86.6%. However, we must consider the possible false negative results that may occur in some histological types of PTC.