• Luca Giovanella, Luca Ceriani, Sergio Suriano, Antonella Ghelfo, and Marco Maffioli.
• Department of Nuclear Medicine and Thyroid Unit, Oncology Institute of Southern Switzerland, CH-6500 Bellinzona, Switzerland. luca.giovanella@eoc.ch
• Clin. Endocrinol. (Oxf). 2008 Oct 1; 69 (4): 659-63.

AimThyroidectomy 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.MethodsWe 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.ResultsA 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. ConclusionsBased 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.

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