Radioiodine total body scan versus serum thyroglobulin levels in follow-up of patients with thyroid cancer.

Two groups of patients were studied to compare the efficacy of serum thyroglobulin (Tg) levels to 131I total body scans in the follow-up of patients with thyroid cancer. All of the group of 30 patients without recurrence had undetectable Tg levels on and off thyroid hormone replacement, and all had negative total body scan results although eight patients showed uptake in remnant thyroid tissue. In the second group of 37 patients with documented recurrent or metastatic disease, 34 (92%) had positive serum Tg levels, although the levels in five of these patients were undetectable while on thyroid replacement, and 31 (84%) had positive total body scan results. The false negative results of the two tests were not overlapping, and of those with positive Tg levels, 29 showed a significant increase once thyroid hormone therapy had been withdrawn. We conclude that although the percentages of positive Tg levels and body scan results in patients with recurrent disease are similar, both tests are required to minimize the number of patients with undiagnosed metastases. Second, thyroid-stimulating hormone suppression has a definite although unpredictable effect on serum Tg levels in patients with thyroid cancer, and thyroid hormone should be withdrawn prior to measurement of serum Tg to minimize the number of false negative results.