Most patients who have undergone thyroidectomy and RAI ablation and have a negative whole body scan and a stimulated Tg level in the range of 2–10 ng/mL will see their Tg level decline to an undetectable level, so they probably should not be treated subsequently with RAI, Dr. Tuttle advised. It is likely that “if you do nothing, you are going to take credit for this thyroglobulin number going down over time all by itself.”
It is not necessary to treat patients with high Tg levels with two to three doses of RAI, he added. In a study of 17 patients with a negative initial whole body scan and an elevated Tg level, 16 patients had a positive scan after RAI therapy. During the course of three subsequent RAI doses, the percentage of patients with a decreasing Tg level increased from 81% to 90% to 100%, but the mean stimulated Tg level only decreased from 74 to 62 to 32 ng/mL, respectively (J. Clin. Endocrinol. Metab. 1995;80:1488–92).
Low Tg: RAI Probably Not Helpful
To determine if follow-up RAI therapy contributes to any changes in the stimulated Tg level of patients with an initial stimulated Tg level below 10 ng/mL, Dr. Tuttle conducted a study of 110 thyroid cancer patients who had Tg levels between 0.6 and 10 ng/mL and a negative whole body scan 1 year after receiving a total thyroidectomy and RAI ablation. At that point, 18 patients received repeat RAI therapy and 92 were observed.
After 1–2 years, stimulated Tg levels subsequently decreased in 71% and became undetectable in 29% of patients who had an initial stimulated Tg level between 0.6 and 2 ng/mL. In patients with an initial stimulated Tg level between 2 and 10 ng/mL, a significantly lower percentage of patients (3%) had an undetectable stimulated Tg level than those who had a decreased level (42%).
But among observed and RAI-treated patients with an initial stimulated Tg level between 2 and 10 ng/mL, there was no significant difference in the percentage of patients who had a reduction (40% vs. 45%, respectively), no change (12% vs. 18%), or an increase (48% vs. 37%) in their stimulated Tg level at follow-up.