Serum thyroglobulin levels at the time of 131I remnant ablation just after thyroidectomy are useful for early prediction of clinical recurrence in low-risk patients with differentiated thyroid carcinoma

We investigated whether serum thyroglobulin (Tg) measured at the time of remnant ablation (ablation-Tg) could be a prognostic indicator complementary to serum Tg levels at the time of the first diagnostic whole-body scan (WBS) after thyroid hormone withdrawal (control-Tg; approximately 6 - 12 months after ablation-Tg) and whether ablation-Tg could predict the persistence or recurrence of disease in low-risk patients with differentiated thyroid carcinoma. Patients with differentiated thyroid carcinoma ( n = 268) treated with total or near-total thyroidectomy followed by immediate I-131 remnant ablation were studied. Patients with anti-Tg autoantibodies and those showing evidence of extracervical metastases were excluded. Two patients showing remnant uptake on follow-up diagnostic WBS received a second ablation. We found significant correlation between ablation-Tg and control-Tg levels; 114 of 143 patients (80%) with ablation-Tg greater than 2 mu g/liter showed detectable (>= 1 mu g/ liter) control-Tg, and 70 of 125 (56%) patients with ablation-Tg 2 mu g/liter or less showed undetectable (< 1 mu g/liter) control-Tg [ odds ratio 5.1, 95% confidence interval (CI) 3.0 - 8.9, P< 0.001]. When the 268 patients were followed up for a mean period of 5.7 +/- 1.4 yr ( range 2.8 - 8.3 yr), 35 (13%) had recurrences; 73 27%) were classified as "Tg positive, no evidence of disease"; and 160 (60%) showed complete remission. Of 143 patients with ablation-Tg greater than 2 mu g/liter, recurrence was observed in 33 cases (23%); " Tg positive, no evidence of disease," was observed in 52 cases (36%); and complete remission was observed in 58 cases (41%). Of 125 patients with ablation-Tg 2 mu g/liter or less, two patients (2%) showed recurrence during the follow-up; 21 patients (17%) were regarded as " Tg positive, no evidence of disease"; and 102 patients (81%) showed complete remission. The positive predictive value for recurrence in patients having ablation-Tg greater than 2 mu g/liter was found to be 23.1% ( 33 of 143 patients, 95% CI 16.4 - 30.8%). The negative predictive value for recurrence in patients having ablation- Tg 2 mu g/liter or less was found to be 98.4% ( 123 of 125 patients, 95% CI 94.4 - 99.8%). These data indicate that serum Tg levels measured at the time of immediate postoperative I-131 remnant ablation correlated well with serum Tg levels at the time of the initial diagnostic WBS and had a complementary role for predicting persistence or recurrence of disease in the earliest postoperative period.