Context: In preparation for whole body radioactive iodine scanning, recombinant human TSH (rhTSH) is usually administered as 0.9 mg intramuscular injections on two consecutive days without regard to age, body size or other co-morbid conditions.

Objective: Our objective was to determine if 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 following thyroid hormone withdrawal, and 19 following rhTSH).

Main Outcome Measures: The dynamic time course of serum TSH changes following 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/L, range 110-452 mIU/L) and in those prepared with rhTSH (134 ± 75 mIU/L, range 32-290 mIU/L, P = 0.07).

Serial determinations following rhTSH injections revealed a mean serum TSH (range) of 268 ± 76 mU/L (87 - 628) at 6 h, and 130 ± 58 mU/L (67 - 250) at 24 h after the initial injection; and 361 ± 78 mU/L (161-524) at 6 h, and 134 ± 44 mU/L (32-290) at 24 h after the second injection.

Conclusions: The mean TSH levels achieved in children following 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.