Diagnostic iodine-131 whole-body scan ((131)I-WBS) and serum thyroglobulin values (Tg) performed 6 to 12 months after thyroid ablation for differentiated thyroid carcinoma were evaluated in 194 consecutive patients at the Hospital de Navarra, (Pamplona, Spain). All patients underwent near-total thyroidectomy and (131)I ablation with 3.7 GBq. Patients with positive anti-Tg antibodies or with (131)I uptake outside the neck were previously excluded. Uptake of (131)I in the thyroid bed was detected in 27 patients (13.9%). Serum Tg levels were below 0.5 ng/mL in 133 patients, ranged from 0.5-10 ng/mL in 39 patients, and was above 10 ng/mL in 22 patients. After a follow-up of 7.7 +/- 3.3 years, persistence of the illness has been observed in 2 patients with undetectable Tg (1.5%), but metastases were not detected in any case. In those with Tg higher than 0.5 ng/mL, 29 of 61 patients had persistence of the disease (47.5%) with evidence of metastases in 15 (24.5%), irrespective of the initial total body scan (131)I uptake. In conclusion, serum Tg levels obtained after thyroid ablation has a good prognostic value and permits the selection of patients for further diagnostic studies, while diagnostic (131)I-WBS performed at that time did not correlate with results of Tg and scarcely provides additional information.

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