Serum Thyrotropin (TSH) Levels after Recombinant Human TSH Injections in Children and Teenagers with Papillary Thyroid Cancer

Context: In preparation for whole body radioactive iodine scanning, recombinant human TSH (rhTSH) is usually administered as 0.9-mg im injections on 2 consecutive days without regard to age, body size, or other comorbid conditions. Objective: Our objective was to determine whether the usual adult rhTSH dosing regimen would result in excessive elevations of serum TSH in children and teenagers with thyroid cancer. Design/Setting/Patients/Interventions: A retrospective review identified 53 children and teenagers with thyroid cancer who underwent whole body radioactive iodine (RAI) scanning over a 12-yr period at two major medical centers (34 after thyroid hormone withdrawal and 19 after rhTSH treatment). Main Outcome Measures: The dynamic time course of changes in serum TSH after rhTSH administration and/or hypothyroid withdrawal was examined. Peak TSH levels were correlated with age, weight, and body surface area. Results: The mean serum TSH at the time of RAI administration was similar in patients undergoing hypothyroid preparation (188 ± 118 mIU/liter; range, 110–452 mIU/liter) and those treated with rhTSH (134 ± 75 mIU/liter; range, 32–290 mIU/liter; P = 0.07). Serial determinations after rhTSH injections revealed a mean serum TSH of 268 ± 76 mU/liter (range, 87–628) at 6 h and 130 ± 58 mU/liter (range, 67–250) at 24 h after the initial injection, and 361 ± 78 mU/liter (range 161–524) at 6 h and 134 ± 44 mU/liter (range, 32–290) at 24 h after the second injection. Conclusions: The mean TSH levels achieved in children after rhTSH injections are remarkably similar to values previously reported in adults despite marked differences in clinical characteristics between children and adults. These data suggest that dose adjustments are not generally required in children and teenagers undergoing rhTSH stimulation for RAI scanning or serum-stimulated thyroglobulin determinations.