title: Reference limit of thyrotropin (TSH) and free thyroxine (FT4) in thyroperoxidase positive and negative subjects: a population based study.
abstract: BACKGROUND
  Current reference values for thyroid function tests are based on data from different ethnicities and geographical areas. The aim of the present study was to determine reference intervals for thyrotropin (TSH) and free T4 (FT4), based on the criteria of the National Academy of Clinical Biochemistry (NACB) in an Iranian population.
  
  
  METHODS
  This study was conducted within the framework of Tehran Thyroid Study (TTS), an ongoing prospective cohort of 5704 randomly selected individuals, age ≥ 20 yr. A total of 2199 individuals (43.3% male, 56.7% female), based on NACB criteria were included in this study. Reference limit analysis was performed for the negative thyroid peroxidase antibody (TPOAb) group.
  
  
  RESULTS
  After applying all exclusion criteria except TPOAb positivity (10.5%), data of 2459 participants remained for analysis. Of these, 953 (43.3%) were males and 1246 (56.7%) were females; the mean ± SD age was 43.53 ± 14.16 yr. The mean ± SD and median+IQR for TSH were 1.77 mU/l ± 1.24 and 1.46 (0.93-2.23) mU/l, respectively. The 2.5th and 97.5th percentiles TSH were 0.32 mU/l and 5.06 mU/l respectively. The mean ± SD and median (IQR) for FT4 for all negative TPOAb subjects were 1.19 ± 0.16 and 1.18 (1.08-1.31) ng/dl respectively.
  
  
  CONCLUSIONS
  Reference ranges for thyroid function tests need to be derived from national databases. This study determined age and sex specific TSH and FT4 reference ranges in a Tehranian population, which could eventually enable clinicians to classify patients more appropriately.
authors.affiliation: Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, I.R. Iran.
authors.forename: A
authors.initials: A
authors.lastname: Amouzegar
authors.forename: H
authors.initials: H
authors.lastname: Delshad
authors.forename: L
authors.initials: L
authors.lastname: Mehran
authors.forename: M
authors.initials: M
authors.lastname: Tohidi
authors.forename: F
authors.initials: F
authors.lastname: Khafaji
authors.forename: F
authors.initials: F
authors.lastname: Azizi
mesh_terms: D000328:Adult; D000368:Aged; D001323:Autoantibodies; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000276:immunology; D007492:Iran; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012016:Reference Values; D013961:Thyroid Gland / Q000276:immunology; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D044465:White People
chemical_list: D001323:Autoantibodies; C056626:thyroid microsomal antibodies; D013972:Thyrotropin; D007453:Iodide Peroxidase; D013974:Thyroxine