Thyroglobulin in differentiated thyroid cancer

Identification of differentiated thyroid cancer (DTC) is becoming increasingly common. Patients usually have an excellent prognosis. Most undergo total thyroidectomy, radioiodine ablation and treatment with suppressive doses of levothyroxine. Patients require long term follow-up which includes measurement of serum thyroglobulin (Tg). Interpretation of serum Tg requires knowledge of the concurrent thyroid stimulating hormone (TSH) concentration, as secretion is TSH dependant, and an awareness of the limitations of the methods used to measure it. These limitations include the heterogeneity of Tg in serum, the ability of assays to recognise forms of Tg secreted by a tumour, assay biases and not least the potential for interference in immunoassays for Tg from endogenous thyroglobulin antibodies (TgAbs) in patient serum. This review considers what the clinician wants to know and how Tg results can be interpreted in light of an awareness of assay limitations. •Serum thyroglobulin (Tg) is a useful tumour marker for the follow up of patients with differentiated thyroid cancer.•Measurement of Tg by immunoassay has several limitations: heterogeneity of Tg, interference from endogenous Tg antibodies (TgAbs), Tg assay bias.•Interpretation requires knowledge of thyroid stimulating hormone (TSH) concentration and an awareness of the limitations of Tg measurement•Laboratory investigations to identify assay interference are reviewed•Interpretation of Tg results and what to do if results do not fit with the clinical picture are discussed.•The optimal management of patients with DTC requires close working of a multidisciplinary team and awareness of the inherent limitations of Tg measurement.