Clinical value of TSH-stimulated thyroglobulin in evaluation of metastasis from differentiated thyroid carcinoma after 131I treatment

Objective To investigate the critical value of TSH-stimulated Tg(sTg) in the diagnosis of metastasis from DTC, and to evaluate the diagnostic value of the ratio of sTg to suppressed Tg (sTg/suppressed Tg). Methods A total of 330 post-operative DTC patients(87 males, 243 females, age range: 12-70 years)who underwent thyroid remnant ablation from August 2008 to December 2014 were retrospectively reviewed. Their serum TgAb levels were normal. The patients were divided into non-metastasis group(147 cases)and metastasis group(183 cases) according to results of ultrasonography, CT and WBS. The difference of sTg between the two groups were compared by Mann-Whitney rank sum test. ROC curve was used to analyze the relationship between sTg, sTg/suppressed Tg ratio and metastasis, the cutoff value was calculated. Results The sTg was significantly different between the non-metastasis group and metastasis group: 1.0 (0.1, 2.0) μg/L vs 36.5 (3.9, 126.7) μg/L; u=-6.642, P<0.05. The AUC for ROC curve in metastasis group was 0.85, and the cutoff value was 2.05 μg/L, with the sensitivity 85.2%, specificity 67.3%, and accuracy 82.3%. While sTg<2.05 μg/L, the AUC of sTg/suppressed Tg ratio was 0.941, and the cutoff value was 4.3, with the sensitivity 93.3%, specificity 88.2%, and accuracy 92.3%. Conclusions The sTg has a specific value for the diagnosis of metastasis from DTC after operation and the cutoff value is 2.05 μg/L in this set of patients. The ratio of sTg/suppressed Tg could be used to correct the sTg and to improve the diagnostic sensitivity. Key words: Thyroid neoplasms; Neoplasm metastasis; Radiotherapy; Iodine radioisotopes; Thyroglobulin