Rapid rise in serum thyrotropin concentrations after thyroidectomy or withdrawal of suppressive thyroxine therapy in preparation for radioactive iodine administration to patients with differentiated thyroid cancer.

Patients with differentiated thyroid cancer are often treated transiently with T(3) in preparation for radioactive iodine (RAI) therapy. We questioned the value of using T(3) transiently in patients requiring RAI therapy. Two groups of patients requiring RAI therapy were investigated. One group included patients studied immediately after thyroidectomy, whereas the other included those withdrawn from chronic suppressive T(4) therapy that followed thyroidectomy and postoperative RAI ablation. Serum TSH concentrations were serially measured two to three times weekly until they reached more than 30 mU/liter, after which RAI therapy was administered. Serum TSH concentrations reached more than 30 mU/liter 8-26 d (mean +/- sd, 14.2 +/- 4.8) after thyroidectomy or 9-29 (18.1 +/- 4.1) d after T(4) withdrawal. That level of TSH elevation was achieved 18 d after thyroidectomy and 22 d after T(4) withdrawal in more than 95% of patients. Minimal symptoms of hypothyroidism were noted in either group when RAI was administered. Serum TSH concentrations increased rapidly without transient therapy with T(3). To minimize symptoms of hypothyroidism, serum TSH levels should be measured twice weekly, starting 10 d after thyroidectomy or T(4) withdrawal. The data cast doubt about the value and benefits from using T(3) in preparing patients for RAI therapy.