Thyroglobulin measurement in fine-needle aspirates of lymph nodes in patients with differentiated thyroid cancer.

Background: The high incidence of cervical lymph nodes metastasis in highly differentiated thyroid carcinoma (DTC) and insufficient of existing diagnostic methods determines the urgency of finding reliable and more effective tests. Aims: The aim of our study is to determine the prognostic significance of the thyroglobulin measurement in washout fluid from fine-needle aspiration biopsy (FNA-Tg) and the cut-off value in the diagnosis of DTC lymph nodes metastasis. Materials and methods: 245 patients evaluated for suspicious cervical lymph nodes were retrospectively reviewed. All patients underwent FNA-Tg, serum thyroglobulin (sTg) levels, thyroglobulin antibodies (Tg-Ab), thyroid-stimulating hormone (TSH) were measured. 125 patients with malignant changes according to FNA and/or high FNA-Tgvalues underwent surgical treatment. Patients were divided into 2 groups with reactive ( n = 23) and metastatic ( n = 102) changes. FNA-TG was assayed on automated system Cobas 601 (Roche, France). Results: All patients were comparable by sex, age and levels of TSH, sTG, Tg-Ab. The FNA-Tg median in metastatic group was 537.0 [0.1; 1000], and in benign group – 17.9 [0.5; 158.0], p = 0.003. The sensitivity of isolated FNA was 85%, specificity 57%, AUC = 0.618, 95% CI 0.516–0.713. The sensitivity and specificity of FNA-Tg was 73% and 100%, respectively, AUC = 0.865, 95% CI 0.78–0.92. The optimal cut-off point for malignancy was >9.2 ng/ml (sensitivity 75%, specificity 100%), Youden Index 0.73. Conclusions: Additional FNA-Tg may increase the sensitivity of isolated FNA in evaluation of DTC lymph node metastasis. The optimized cut-off value >9.2 ng/ml can be proposed as a diagnostic threshold for the definition of malignancy.