Prognostic Value of Thyroglobulin Serum Levels and 131I Whole-Body Scan after Initial Treatment of Low-Risk Differentiated Thyroid Cancer

Abstract and Introduction

Diagnostic iodine-131 whole-body scan (¹³¹I-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 ¹³¹I ablation with 3.7 GBq. Patients with positive anti-Tg antibodies or with ¹³¹I uptake outside the neck were previously excluded. Uptake of ¹³¹I 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 ¹³¹I 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 ¹³¹I-WBS performed at that time did not correlate with results of Tg and scarcely provides additional information.

In most centers, the usual treatment of differentiated thyroid cancer consists of total or near-total thyroidectomy, followed by ablation of residua with high-dose ¹³¹I, and levothyroxine therapy in sufficient doses to maintain suppressed thyrotropin (TSH) levels.^[1,2] Follow-up is based on ¹³¹I whole-body scans (¹³¹I-WBS) and the determination of serum thyroglobulin (Tg) levels, after suspension of levothyroxine during a period sufficient enough to allow for substantial increment of TSH levels, with the aim of detecting possible persistence of thyroid tissue either locally or distant metastases.^[3,4]

With improvements in methods of determination of serum Tg levels, it has been observed that if antithyroglobulin autoantibodies (anti-TgAb) are negative, there is an excellent correlation between the Tg levels and persistence of disease.^[5,6] In most cases, undetectable Tg levels suggest absence of either thyroid tissue or distant metastases, thus complete remission.

Recently, coinciding with the availability of recombinant human TSH, which obviates the withdrawal of levothyroxine,^[7–9] various groups have proposed the withdrawal of ¹³¹I-WBS in the follow-up of low-risk patients who have had a prior negative scan, given that it does not provide any additional clinical information to that obtained from the determination of Tg levels with high TSH.^[10,11]

We have analyzed the serum Tg levels and ¹³¹I-WBS results in our series after total thyroidectomy and remnant ¹³¹I ablation in relation to the clinical evolution, persistence, or recurrence of the disease.

Thyroid. 2004;14(4) © 2004 Mary Ann Liebert, Inc.

Cite this: Prognostic Value of Thyroglobulin Serum Levels and 131I Whole-Body Scan after Initial Treatment of Low-Risk Differentiated Thyroid Cancer - Medscape - Apr 01, 2004.