[Value of serum thyroglobulin assays in cancers of the thyroid]

Serum thyroglobulin (Tg) assays provide no clue as to the nature of a cold thyroid nodule, but they provide guidelines for isotope exploration tests in differenciated epitheliomas. Undetectable Tg levels during hormonal treatment make these tests unnecessary, while measurable levels in the absence of residual thyroid tissue should encourage investigations for metastases, and the higher these levels the more thorough the investigation. When thyroid residues are present Tg levels are usually within the normal range for a healthy population (2.5-28 ng/ml) and no conclusion can be drawn. The destruction of thyroid residues with Iodine 131 in poor prognosis patients facilitates monitoring by means of Tg assays.