Thyroglobulin washout from cervical lymph node fine needle aspiration biopsies in patients with differentiated thyroid cancer: an analysis of different expressions to use in post-total thyroidectomy follow-up.

Introduction: Although frequently used as an adjunct to cytology in patients with differentiated thyroid cancers, interpretation of thyroglobulin washout remains unclear. We aim to compare the utility of different analytic tools to develop recommendations for use in post-total thyroidectomy follow-up.

Methods: This is an institutional review board-approved retrospective study of patients who underwent lymph node fine needle aspiration biopsy with thyroglobulin washout between 2012 and 2018, during the post-total thyroidectomy follow-up of differentiated thyroid cancer. The utilities of thyroglobulin washout concentration, thyroglobulin washout/serum thyroglobulin ratio, and absolute thyroglobulin content were compared.

Results: Sixty-four patients underwent 79 fine needle aspirations with thyroglobulin washout of cervical lymph nodes. Fifty-two lymph nodes were found to be metastatic and 27 benign. One patient had a pathologically confirmed lymph node metastasis despite a thyroglobulin washout of 0. The optimal cutoffs of thyroglobulin washout, thyroglobulin washout/serum thyroglobulin ratio, and absolute thyroglobulin content to predict metastatic involvement were 2.5 ng/ml (94% sensitive, 100% specific), 0.1 (100% sensitive and specific), and 12.5 (94% sensitive, 100% specific), respectively. The second measure lacked utility in patients with undetectable serum thyroglobulin.

Conclusion: The use of thyroglobulin washout concentration or thyroglobulin washout/serum thyroglobulin ratio has drawbacks based on variations in technique and clinical scenario. Absolute thyroglobulin content is an alternative that may be a more objective expression of thyroglobulin washout.