The usefulness of detecting thyroglobulin in fine-needle aspirates from patients with neck lesions using a sensitive thyroglobulin assay.

The aim of this study was to assess the diagnostic utility of thyroglobulin (Tg) in fine needle aspirates (Tg-FNAB) of nonthyroidal neck masses using a sensitive in-house method for detecting Tg in washout specimens. A total of 256 samples from 145 patients were evaluated for Tg in washout specimen from FNAB and compared to corresponding cytological smear and histology of 46 surgical specimens. Tg was measured by a sensitive in-house time-resolved immunofluorometric assay. The sensitivity for Tg-FNAB alone or in combination with cytological findings was found to be 100% in both the follow-up group and before primary surgery. In the follow-up group the specificity of Tg-FNAB was 100%. Fifty-nine of 60 follow-up specimens with malignant cytology were Tg-FNAB positive (n = 195). Histological examination of one lymph node with malignant cytology and negative Tg-FNAB showed metastasis from carcinoma of the salivary gland. Tg-FNAB was positive in 25 specimens with suspicious or cystic cytology. Tg-FNAB values were high (median 4557 microg/l, range 122-37200 microg/l) in washout specimen from cystic metastasis from which cytology did not confirm malignancy. Of the 20 lymph nodes with histology confirming metastasis from differentiated thyroid carcinoma (DTC), the Tg-FNAB was positive in 19 and intermediate in one. However, before primary surgery, two Tg-FNABs were false positive compared to the histology of the lymph nodes. TgAb in serum did not interfere with FNAB-Tg measurements. Tg-FNAB measurement is accurate with high sensitivity (100%) and of great importance in detecting cystic metastasis when cytology is not conclusive. Even metastases to small neck lymph nodes may be detected by using sensitive Tg-assay. Serum thyroglobulin antibodies appear to have ignorable effect on the clinical performance of Tg-FNAB.