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 cutoff value of FNA-Tg, we conducted a retrospective study of patients with neck masses outside the thyroid which are 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 by the receiver operating characteristic curve. Among 210 lesions, 57 were of thyroid origin and 153 lesions were not thyroid origin. High FNA-Tg value was observed in the lesions with thyroid origin (p:0.001) and the cutoff value at the minimum point of 100% specificity was 32.2 ng/ml and the sensitivity was 87.7%. Regarding the effect of serum anti-Tg antibodies, FNA-Tg values were significantly lower or not significantly different depending on the grouping, and further studies are needed. 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 with that of 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.