Lucy Ding¹, Luka McDonald
¹NSW Health Pathology

Accurate thyroglobulin (Tg) measurement is essential for monitoring recurrence in patients with differentiated thyroid cancer (DTC) post-thyroidectomy and radioactive iodine ablation. Traditional immunoassays (Tg-IA) are prone to interference by anti-thyroglobulin antibodies (TgAbs), affecting about a third of patients with DTC and potentially causing falsely low or undetectable Tg levels. This interference can result in under-treatment or unnecessary investigations. NSW Health Pathology has developed a Thyroglobulin by Mass Spectrometry (Tg-MS) assay, the first of its kind in Australasia, to reliably quantify Tg even in the presence of TgAbs.

A clinical validation study at Royal North Shore Hospital will evaluate Tg-MS in addressing the limitations of Tg-IA. Patients with detectable TgAbs will undergo Tg-MS alongside Tg-IA measurements over 12 months. For those with discordant results between methods, data from imaging, biopsies, and other investigations will be used to determine which assay better predicts structural disease and assess the impact on clinical management. If successful, Tg-MS could reduce unnecessary investigations, provide reassurance, and enable timely treatment escalation, improving care for patients affected by TgAb interference.