Serum thyroglobulin in the diagnosis and management of thyroid carcinoma.

Serum thyroglobulin (Tg) was measured by radioimmunoassay in sixty-two control subjects, 163 euthyroid patients with nodular goitre and eighty-one patients with previously treated differentiated thyroid carcinoma. Tg was elevated in 65% of nodular goitres and failed to fall with thyroxine treatment in ten/fifteen patients treated. A diagnosis of differentiated carcinoma was confirmed in fourteen/sixty-four of these patients and Tg was elevated in twelve. Of sixty-five treated thyroid carcinoma patients without evidence of residual tumour, serum Tg was undetectable in thirty-nine, normal in twenty-four and elevated in two. There was evidence of residual tissue in the thyroid in seventeen of the patients with detectable Tg. Of the sixteen patients with residual tumour or metastases Tg was elevated in fifteen. There was a positive correlation between goitre size and Tg levels in multinodular goitre, and thyroid carcinomas of large bulk were associated with higher Tg levels. Serum Tg was normal in medullary carcinoma and in two patients with thyroid metastases from extra-thyroidal malignancies. High Tg levels in patients with residual metastases from thyroid carcinoma following thyroid ablation indicates Tg production by tumour tissue. Measurement of serum Tg of limited value in the differential diagnosis of nodular thyroid disease. It is particularly useful following surgery and 131I therapy for differentiated thyroid carcinoma. In these patients it gives confirmation of thyroid albation and may provide evidence of residual tumour tissue when the other tests are negative.