RESUMO
OBJECTIVE: To evaluate two variables affecting Thyroglobulin stability in the washout of fine needle aspiration biopsies of thyroid nodules and metastatic lymph nodes. MATERIALS AND METHODS: Thyroglobulin stability after storage at -20 °C up to 14 days was studied in washout performed with normal saline solution and further dilutions with normal saline solution from five metastatic thyroid nodes and six benign thyroid nodules. We also studied thyroglobulin stability in diluents compared with normal saline solution: 4% bovine serum albumin in normal saline solution and diluents free from thyroglobulin or Calcitonin or parathyroid hormone in paired and simultaneous thyroglobulin measurements of washout dilutions from 5/6 benign thyroid nodules and 2/5 metastatic lymph nodes. Thyroglobulin and Thyroglobulin antibodies were measured by a chemiluminescent assay. Positive samples with thyroglobulin antibodies in serum and/or washout were excluded. RESULTS: Thyroglobulin decreased with storage in washout or dilutions of washout performed in normal saline solution (p < 0.05). Lower thyroglobulin concentrations, close to the commonly used cut-off (1.1 ng/mL), showed the highest decrease as soon as after 1 day of storage. Diluents other than normal saline solution stabilized thyroglobulin in dilutions of all washout. CONCLUSIONS: The results suggest that the reliability of thyroglobulin measurements in washout of fine needle aspirates could be preserved by immediate measure of thyroglobulin or the use of stabilizing diluents to perform washout.