Aim: Thyroidectomy followed by administration of large activities of 131-iodine ((131)I) is the treatment of choice for differentiated thyroid carcinoma (DTC). The serum thyroglobulin (Tg) measurement during hypothyroidism (offT4-Tg), just before radioiodine thyroid ablation, has proved to be effective for predicting persistent/recurrent disease. However, the Tg measurement cannot be used as a corresponding value for pre-ablative offT4-Tg when recombinant human TSH (rhTSH) is used as stimulus before treatment. The present study was undertaken to evaluate if post-thyroidectomy Tg values, measured before rhTSH-stimulated radioiodine ablation is of prognostic value in patients affected by DTC.

Methods: We enrolled 126 patients with DTC submitted to total thyroidectomy. T4 treatment was started just after surgery to suppress TSH levels and Tg levels (onT4-Tg) were measured just before rhTSH-aided thyroid ablation by (131)I (3700 MBq). Neck radioiodine uptake (RAIU) was measured just before ablation and a post-treatment whole body scan (PT-WBS) was performed.

Results: A significant relationship was found between thyroid remnants' RAIU and onT4-Tg levels (P < 0.001). The 1.10 ng/ml onT4-Tg threshold selected by ROC curve analysis identifies patients with positive PT-WBS with 83.3% sensitivity, 65.7% specificity, 44.5% positive predictive value (PPV) and 93.6% negative predictive value (NPV). The 0.65 ng/ml cut-off level recognizes metastatic patients with 82.9% sensitivity, 55.2% specificity, 43.3% PPV and 97.8% NPV when compared with 12 months restaging results. Among 63 patients with initially undetectable onT4-Tg (i.e. <or= 0.2 ng/ml) none had positive PT-WBS nor DTC relapse at 12-month restaging (NPV 100%).

Conclusions: Based on our data we conclude that pre-ablative onT4-Tg is a prognostic marker and should be used instead of pre-ablative TSH-stimulated Tg measurement when rhTSH-aided radioiodine ablation is done.