A comparison of the effectiveness of 131I whole body scans and plasma Tg determinations in the diagnosis of metastatic differentiated carcinoma of the thyroid: a retrospective study

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Abstract
In 68 patients with proved metastases of differentiated thyroid carcinoma the comparative value of the 131I whole body scan and plasma Tg measurements in establishing the diagnosis of metastasis or recurrence was analyzed retrospectively. At the time of primary therapy most metastases were diagnosed by the post-therapy scan (78%). Eight of 9 scintigraphic negative metastases in the post-therapy scan were indicated by elevated Tg levels (> 10 ng/ml). Twenty-four of 28 recurrences after a disease free interval were negative in the 2 mCi 131I scan, 18 of these patients were Tg positive. Of the 4 recurrences with positive 131I uptake all were Tg positive; two of them only during endogenous TSH stimulation. It is conlcuded that the routine 2 mCi whole body scan is less efficient in follow-up than is generally assumed. The most important follow-up parameter for these patients is the plasma Tg which can be obtained under suppressive therapy if a sensitive assay is used. In patients with a negative post-therapy scan and a negative Tg (< 5 ng/ml) it seems justified to omit further 131I whole body control scans as long as Tg remains negative.

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