Cutoff value of thyroglobulin in needle aspirates for screening neck masses of thyroid carcinoma

Measurement of thyroglobulin in fine-needle aspirates (FNA-Tg) is useful for the diagnosis of lymph node metastasis in thyroid carcinoma; however, the cutoff value remains unclear, particularly for the differential diagnosis of neck masses. To evaluate the cutoff value of FNA-Tg, we conducted a retrospective study of patients with neck masses outside the thyroid who pre-operatively underwent both FNAC and FNA-Tg, followed by pathological examination at our hospital from October 2015 to September 2020. The cutoff value of FNA-Tg was calculated using the receiver operating characteristic curve. Among 210 lesions, 57 were of thyroid origin and 153 lesions were not of thyroid origin. A high FNA-Tg value was observed in the lesions of thyroid origin (P: 0.001), and the cutoff value at the minimum point of 100% specificity was 32.2 ng/mL with a sensitivity of 87.7%. Regarding the effect of serum anti-Tg antibodies, FNA-Tg values were significantly lower or not significantly different depending on the grouping, warranting further studies. Among the cases with papillary thyroid carcinoma, the sensitivity of FNAC and FNA-Tg was 71.4% and 87.5%, respectively. The cutoff value of FNA-Tg for the differential diagnosis of neck masses was higher compared to previous reports because some metastatic lymph nodes of carcinomas and lesions, other than lymph nodes, exhibited higher FNA-Tg values. Therefore, if FNA-Tg is to be used as a screening test for the differential diagnosis of neck masses in patients without proven thyroid carcinoma, it is necessary to establish a higher cutoff value.