The value of thyroglobulin (Tg) measurement in fine needel aspirates of neck lymph nodes in differentiated thyroid carcinoma is not affected by anti-Tg antibodies.

Serum thyroglobulin (Tg) is the most useful marker in the follow-up of patients after total thyroidectomy for differentiated thyroid carcinoma (DTC), but its usefulness is limited by the interference of serum anti-Tg antibodies (TgAb). Detection of Tg in the needle wash-out of fine-needle aspiration biopsy (Tg-FNAB) is also a very useful tool to identify metastatic neck lymph nodes in DTC, but, to our knowledge, no study has been carried out to evaluate a possible interference of serum TgAb in this procedure. We have therefore retrospectively reviewed 50 patients (25 after surgery for TC and 25 with suspicious thyroid nodules) referred to our institution for the presence of clinically suspicious cervical lymph nodes. All patients were submitted to ultrasound guided FNAB of neck lymph nodes to obtain cytological examination and detection of Tg in the needle wash-out. Patients were subdivided in two study groups: 18 patients showed detectable serum TgAb (TgAb+), while 32 had undetectable serum TgAb (TgAb-). Based on preliminary study, any Tg concentration >10 ng/ml in FNAB wash-out was considered abnormal. Tg-FNAB, cytological and histological results of surgically removed lymph nodes are showed in the table: GROUPS LYMPH NODES TgAb+ (n=18) Tg-FNAB >10 ng/ml (n=11) Tg-FNAB <10 ng/ml (n=7) Cyto+ (n=9) Cyto- (n=2) Cyto+ (n=0) Cyto- (n=7) Histo+ (n=9) Histo+ (n=2) TgAb-(n=32) Tg-FNAB >10 ng/ml (n=12) Tg-FNAB <10 ng/ml (n=20) Cyto+ (n=9) Cyto- (n=3) Cyto+ (n=5) Cyto- (n=15) Histo+ (n=9) Histo+ (n=3) Histo+ (n=3)* Histo- (n=2) Cyto+: cytology suspect for metastasis; Cyto-: cytology not suspect for metastasis Histo+: presence of metastasis at histology; Histo-:absence of metastasis at histology *All poorly differentiated tumors In conclusion, Tg assay in the needle wash-out of FNAB is not significantly affected by the presence of serum TgAb and this procedure remains superior to cytology in the identification of differentiated nodal metastases even in TgAb+ patients. However, cytology should always be performed, since Tg is undetectable in FNAB from undifferentiated metastases.