Follow-up of patients with differentiated thyroid cancer using serum thyroglobulin measured by an immunoradiometric assay. Comparison with I-131 total body scans.

An immunoradiometric assay for thyroglobulin (Tg), which allows quantification of Tg in the presence of anti- Tg, has been evaluated in patients with differentiated thyroid cancer. All patients had undergone thyroidectomy plus I- 131 ablation. Three separate studies have been conducted. 1. Tg levels were compared with I- 131 whole-body scans made at 48 hr in 22 patient studies. Both tests gave similar results in 19 of the studies, but in three patients the results of the tests were discordant. 2. Tg levels were compared with clinical status in 18 patients who were free of disease; 15 had Tg values < 5 ng/ml, and three had measurable but normal Tg values. Three patients with metastatic disease had measurable Tg, and in two the values were above normal. 3. Sequential Tg measurements were made at intervals of 3 mo in 19 patients on thyroxine. Fifteen of these patients had identical results on two or more occasions.