title: Children with differentiated thyroid cancer achieve adequate hyperthyrotropinemia within 14 days of levothyroxine withdrawal.
abstract: BACKGROUND
  The preparation for radioiodine administration recommended by the current pediatric literature is a 6-wk withdrawal that typically includes the transient administration of T3. Compared with adults, T4 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
  The objective of this study was to determine whether children with differentiated thyroid cancer achieve adequate hyperthyrotropinemia using an abbreviated levothyroxine withdrawal protocol.
  
  
  METHODS
  The study design was a retrospective analysis of 15 consecutive levothyroxine withdrawals performed without T3 at Children's Hospital Boston.
  
  
  METHODS
  Eleven children with differentiated thyroid cancer were included. The average age at the time of withdrawal was 12.5 +/- 0.8 yr.
  
  
  METHODS
  Serum TSH concentrations obtained after the discontinuation of levothyroxine were analyzed to determine the time interval required to achieve a serum TSH level greater than 25 microU/ml for each patient.
  
  
  RESULTS
  Adequate hyperthyrotropinemia was documented in all children tested by d 14. The mean interval required to achieve a serum TSH level above 25 microU/ml from a suppressed serum TSH was 12.3 +/- 0.7 d.
  
  
  CONCLUSIONS
  Shorter withdrawals minimize hypothyroid morbidity and the theoretical risk of decreased 131micro)I residence time from excessive hyperthyrotropinemia. These benefits are amplified in children due to their high incidence of distant metastases. We propose an abbreviated 2-wk withdrawal protocol to facilitate the adjunctive therapy and surveillance of children with follicular cell-derived cancers.
authors.affiliation: Harvard Institutes of Medicine, 77 Avenue Louis Pasteur, Room 642, Boston, Massachusetts 02115, USA.
authors.forename: Wichert J
authors.initials: WJ
authors.lastname: Kuijt
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Huang
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000097:blood / Q000532:radiotherapy*; D000293:Adolescent; D002648:Child; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000097:blood / Q000532:radiotherapy*; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000494:pharmacology*
chemical_list: D007457:Iodine Radioisotopes; D013972:Thyrotropin; D013974:Thyroxine