title: Thyroxine screening values in premature infants.
abstract: OBJECTIVE
  Premature infants often have low thyroxine levels when compared to fullterm infants. We sought to determine gestational age specific normal ranges for thyroxine screening results for premature infants in neonatal intensive care units.
  
  
  METHODS
  Thyroid screening results for infants less than 38 weeks gestation admitted to two NICUs were examined. For each sample the thyroxine Z-score was computed using parameters from fullterm infants. The mean thyroxine Z-score was calculated for each gestational age for days of life 1, 2, 3-7, 8-14, 15-21, 22-28, and 29-60.
  
  
  RESULTS
  There were 1144 specimens obtained from 543 premature infants. The mean thyroxine Z-score was below 0 for almost every gestational age and days-of-life category. The mean thyroxine Z-score increased with gestational age, but did not rise with increasing postpartum age.
  
  
  CONCLUSIONS
  The data show that normal thyroxine Z-scores for premature infants are lower than for fullterm infants and remain low at least as long as the infants remain ill.
authors.affiliation: Department of Pediatrics, Children's Regional Hospital, Cooper Hospital/University Medical Center, Robert Wood Johnson Medical School at Camden, NJ 08103, USA.
authors.forename: J
authors.initials: J
authors.lastname: Saslow
authors.forename: E M
authors.initials: EM
authors.lastname: Post
authors.forename: C A
authors.initials: CA
authors.lastname: Southard
authors.forename: G M
authors.initials: GM
authors.lastname: Stuart
authors.forename: M
authors.initials: M
authors.lastname: Fernandes D'Souza
mesh_terms: D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D015997:Neonatal Screening; D012189:Retrospective Studies; D013974:Thyroxine / Q000097:blood*
chemical_list: D013974:Thyroxine