Many now advocate undertaking follow-up measurements of serum thyroglobulin levels. Metastases from differentiated papillary and follicular thyroid carcinomas are associated with a raised serum thyroglobulin level of more than 10┬╡g/ml in patients with an ablated thyroid that is maintained on T4 replacement. Alternatively, provided that no normal thyroid tissue is present, serum thyroglobulin may be measured two weeks after withdrawal of maintenance T3 or four to six weeks after withdrawal of T4. A raised thyroglobulin level in the follow-up after initial treatment is an indication to determine the presence of metastatic disease. In general, a consecutive series of thyroglobulin assays, together with clinical assessment, can prove sufficient follow-up in many cases. Metastases, however, may rarely be present despite undetectable thyroglobulin levels.
