The value of thyroglobulin (tg) measurement in fine needle aspiration biopsy (FNAB) of neck lymph nodes in differentiated thyroid carcinoma is not affected by anti-tg antibodies.

Boi F;Baghino G;Atzeni F;Lai ML;Faa G;Mariotti S.

2005-01-01

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Abstract

OBJECTIVE: serum Tg is a specific marker in differentiated thyroid carcinoma (DTC) after total thyroidectomy, but its value in patients with serum anti-Tg antibodies (TgAb) is limited by the interference of TgAb in Tg assays. Detection of Tg in needle wash-out of FNAB (Tg-FNAB) is used to identify metastatic neck lymph nodes in DTC, but, to our knowledge, the interference of serum TgAb in this procedure is unknown. SUBJECTS AND METHODS: we have retrospectively reviewed 73 patients (41 after surgery for thyroid cancer and 32 with thyroid nodules) with suspicious cervical lymph nodes. Tg was assayed by IRMA or chemiluminescent assays in ultrasound-guided FNAB used for cytology. According to preliminary data obtained from reactive lymphoadenitis submitted to FNAB, any Tg-FNAB >1 ng/ml in thyroidectomized patients or >36 ng/ml in the presence of thyroid gland were considered as positive for metastasis. Serum TgAb were detected by chemiluminescent or RIA assays. RESULTS: in 51 TgAb-negative patients, Tg-FNAB exceeded the cut-off values in 15 (12 with malignant and 3 with not-diagnostic cytology), all with histologically confirmed DTC metastasis. Of the remaining 36 TgAb-negative patients with Tg-FNAB < cut-off, 30 had not-suspicious and 6 suspicious cytology. The latter were operated and 4 had poorly differentiated thyroid cancer metastases. In 22 TgAb-positive patients, Tg-FNAB exceeded the cut-off values in 14 (12 with malignant and 2 with not-diagnostic cytology), all with histologically confirmed DTC metastasis. In this group no suspicious cytology in the presence of negative Tg-FNAB was observed. CONCLUSIONS: Tg-FNAB is not affected by the presence of serum TgAb and this procedure remains superior to cytology in the identification of DTC nodal metastases. However, cytology should always be performed, since, independently form TgAb, Tg is undetectable in FNAB from poorly differentiated metastases.