title: Area under the curve of TSH after levothyroxine withdrawal versus administration of recombinant human TSH (rhTSH): possible implications for tumor growth.
abstract: OBJECTIVE
  The levothyroxine withdrawal (L-T4) for some weeks results in prolonged exposure to elevated TSH. In contrast, administration of recombinant human TSH (rhTSH) promotes a short period of hyperthyrotropinemia. The objective of this study was to compare the area under the curve (AUC) of TSH obtained after L-T4 withdrawal versus administration of rhTSH.
  
  
  METHODS
  Thirty patients received 0.9 mg rhTSH for two consecutive days, and 64 were prepared by L-T4 withdrawal for four weeks, with the latter being reintroduced 48 hour after 131I. Measurement of TSH were performed before the first rhTSH ampoule; immediately before and seven and 14 days after 131I; before L-T4 withdrawal; and, weekly, up to two months after 131I.
  
  
  RESULTS
  The AUC obtained after rhTSH was 4.6 times smaller than that obtained after L-T4 withdrawal (532 versus 2,423 mIU/L per day). It should be emphasized that, on average, in the latter group, 58.5% of the AUC corresponded to the period after reintroduction of hormone therapy.
  
  
  CONCLUSIONS
  Surprising difference in the TSH AUC was demonstrated between rhTSH administration versus L-T4 withdrawal.
authors.affiliation: Departamento de Tireoide, Santa Casa de Belo Horizonte, Belo Horizonte, MG, Brasil. pedrorosario@globo.com
authors.forename: Pedro Weslley
authors.initials: PW
authors.lastname: Rosario
authors.forename: Daniela Santos
authors.initials: DS
authors.lastname: Salles
authors.forename: Saulo
authors.initials: S
authors.lastname: Purisch
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D019540:Area Under Curve; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011994:Recombinant Proteins / Q000008:administration & dosage; D018709:Statistics, Nonparametric; D013964:Thyroid Neoplasms / Q000097:blood / Q000188:drug therapy* / Q000556:secondary; D013972:Thyrotropin / Q000008:administration & dosage* / Q000097:blood; D013974:Thyroxine / Q000008:administration & dosage*; D028761:Withholding Treatment; D055815:Young Adult
chemical_list: D011994:Recombinant Proteins; D013972:Thyrotropin; D013974:Thyroxine