Context: The preparation for radioiodine administration recommended by the current pediatric literature is a six week withdrawal that typically includes the transient administration of triiodothyronine. Compared with adults, thyroxine clearance rates and serum TSH to free T4 ratios are higher in children, implying that pediatric patients can achieve adequate hyperthyrotropinemia with shorter levothyroxine withdrawals.

Objective: To determine if children with differentiated thyroid cancer achieve adequate hyperthyrotropinemia using an abbreviated levothyroxine withdrawal protocol.

Design: Retrospective analysis of fifteen consecutive levothyroxine withdrawals performed without triiodothyronine at Children's Hospital Boston.

Patients: Eleven children with differentiated thyroid cancer were included. The average age at the time of withdrawal was 12.5 +/- 0.8 yr.

Main Outcome Measurement: Serum TSH concentrations obtained after the discontinuation of levothyroxine were analyzed to determine the time interval required to achieve a serum TSH >25 µU/ml for each patient.

Results: Adequate hyperthyrotropinemia was documented in all children tested by day 14. The mean interval required to achieve a serum TSH >25 µU/ml from a suppressed serum TSH was 12.3 +/- 0.7 days.

Conclusions: Shorter withdrawals minimize hypothyroid morbidity and the theoretical risk of decreased ¹³¹I residence time from excessive hyperthyrotropinemia. These benefits are amplified in children due to their high incidence of distant metastases. We propose an abbreviated 2 week withdrawal protocol to facilitate the adjunctive therapy and surveillance of children with follicular cell-derived cancers.