title: Free thyroxine and thyroid-stimulating hormone reference intervals in very low birth weight infants at 3-6 weeks of life with the Beckman Coulter Unicel DxI 800.
abstract: OBJECTIVE
  To establish reference intervals for thyroid stimulating hormone (TSH) and free thyroxine (FT4) at 3-6 weeks of age in very low birth weight (VLBW) infants with the Beckman Coulter Unicel DxI 800 by gender, birth weight (BW) and gestational age (GA) subgroups.
  
  
  METHODS
  A 4 year retrospective cohort of 308 VLBW infants (GA=27.9 weeks, BW=992.3g) was studied. All blood samples for TSH and FT4 were analyzed using the modified fTSH2 (TSH) and two-step competitive enzyme immunoassay (FT4). Reference intervals were evaluated according to the most recent Clinical and Laboratory Standards Institute (CLSI) guidelines.
  
  
  RESULTS
  The study provides non-parametric 95% reference intervals with associated 90% confidence intervals for FT4 and TSH derived from 308 infants screened at a median of 31 days. The reference intervals for this population are TSH=1.14-11.04 mIU/L and FT4=10.9-21.4 pmol/L. TSH statistically differed according to birth weight (<1000 g vs 1000-1499 g) while FT4 differed according to gender and gestational age at time of testing (<32 weeks vs ≥ 32 weeks); however, these differences were not clinically significant and a single reference interval for each analyte is reported.
  
  
  CONCLUSIONS
  The results of this study highlight the importance and complexity of establishing appropriate reference intervals for thyroid function testing for the preterm population.
authors.affiliation: Division of Neonatology, Children's Hospital of Eastern Ontario (CHEO), 401 Smyth Road, Ottawa, ON K1H 8L1, Canada. Electronic address: xsun@cheo.on.ca.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Sun
authors.affiliation: Department of Obstetrics, Gynecology and Newborn Care, The Ottawa Hospital, 501 Smyth Rd., Ottawa, ON K1H 8L6, Canada.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Lemyre
authors.affiliation: Division of Neonatology, Children's Hospital of Eastern Ontario (CHEO), 401 Smyth Road, Ottawa, ON K1H 8L1, Canada.
authors.forename: Xiaoqin
authors.initials: X
authors.lastname: Nan
authors.affiliation: Division of Neonatology, Children's Hospital of Eastern Ontario (CHEO), 401 Smyth Road, Ottawa, ON K1H 8L1, Canada.
authors.forename: JoAnn
authors.initials: J
authors.lastname: Harrold
authors.affiliation: Department of Pathology and Laboratory Medicine, The Ottawa Hospital, 501 Smyth Rd., Ottawa, ON K1H 8L6, Canada.
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Perkins
authors.affiliation: Division of Endocrinology and Metabolism, CHEO, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Lawrence
authors.affiliation: Children's Hospital of Eastern Ontario Research Institute, Clinical Research Unit, 401 Smyth Road, Ottawa, ON K1H 8L1, Canada.
authors.forename: Nick
authors.initials: N
authors.lastname: Barrowman
mesh_terms: D005260:Female; D006801:Humans; D007231:Infant, Newborn; D019102:Infant, Very Low Birth Weight; D008297:Male; D012015:Reference Standards; D013972:Thyrotropin / Q000097:blood* / Q000592:standards; D013974:Thyroxine / Q000097:blood* / Q000592:standards
chemical_list: D013972:Thyrotropin; D013974:Thyroxine
keywords: Beckman Coulter Unicel DxI 800; FT4; TSH; Very low birth weight infants