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Kyoung Soo Kim  (Kim KS) 1 Article
Serum Thyroglobulin Levels Predicting Recurrence and Distant Metastasis after Surgery in Patients with Differentiated Thyroid Cancer.
Kyoung Soo Kim, Jin Sook Ryu, Suck Joon Hong, Won Bae Kim, Young Kee Shong
J Korean Endocr Soc. 2003;18(2):153-165.   Published online April 1, 2003
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BACKGROUND
Reports on serum thyroglobulin(Tg) levels being used to predict recurrence or distant metastasis during the follow-up of patients with differentiated thyroid cancer(DTC) has been inconsistent. In addition, there have been few reports that attempt to define the cut-off value of Tg for recurrence or distant metastasis obtained by a receiver operating characteristic(ROC) curve. As well, there are differences in opinions on what the value should be on the first serum Tg level measured just before radioactive iodine(RAI) ablation(Tg-RAI), during thyroxine administration (Tg-on), and after thyroxine withdrawal(Tg-off) during the follow-up. Reports on the positive predictive values(PPVs) and negative predictive values(NPVs) of these Tg values are rare. METHODS: A total of 205 patients(42 males, 163 females) with DTC were studied. All patients had undergone total or near-total thyroidectomy. After surgery and RAI ablation, annual thyroxine withdrawal 131I-whole body scan(WBS) with Tg measurements was performed. The mean duration of follow-up was 5.0 (1.4~7.4) years. The most sensitive and specific Tg values(cut-off values) for tumor recurrence and/or distant metastasis were selected by using ROC curves. We also calculated the PPVs and NPVs for recurrence and/or distant metastasis using two-by-two tables. RESULTS: Cut-off values of Tg-RAI, Tg-on, and Tg-off for recurrence were 11.8, 1.4, and 3.3ng/mL, respectively. For these values, the sensitivities were 85.4, 82.2, and 93.3%, with the specificitiesat 89.2, 92.4, and 88.0%. PPVs were 71.9, 77.1, and 77.0% while NPVs were 95.0, 94,4, and 97.8%. The cut-off values for distant metastasis were 27.4, 2.5, and 7.9ng/mL, respectively. For these cut-off values, the sensitivities were 86.7, 87.5, and 92.3%, with the specificities being 86.2, 90.8, and 80.2%. PPVs were 34.2, 46.7, and 25.0% and NPVs were 98.7, 98.8, and 99.3%. CONCLUSION: All three serum Tg levels were sensitive and specific markers for recurrence and distant metastasis. Their PPVs were low in contrast to the high NPVs. In comparison with Tg-on, Tg-off showed higher sensitivity and NPV as well as lower specificity and PPV. Therefore, in the case of higher Tg-on during the follow-up period, efforts to find recurrence and distant metastasis,such as 131I-WBS, should be done. In addition, regular measurement of Tg-off or Tg after stimulation with recombinant human TSH is recommended as a screening test.
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