title: Intraindividual variation in serum thyroid hormones, parathyroid hormone and insulin-like growth factor-1.
abstract: BACKGROUND
  Biological variation of an analyte is an important determinant of its usefulness. Intraindividual variation in serum thyroid hormones, parathyroid hormone (PTH) and insulin-like growth factor-1 (IGF-1) in healthy subjects was determined in this study.
  
  
  METHODS
  Blood samples were taken at weekly intervals for six weeks from 10 healthy subjects and analysed for serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), PTH and IGF-1.
  
  
  RESULTS
  Intraindividual variations for serum FT4 and FT3 were <5.0%, IGF-1 9.4% and TSH and PTH 25.1% and 25.9%, respectively. Index of individuality was lowest for FT4 (0.42) and FT3 (0.38), and highest for PTH (1.09).
  
  
  CONCLUSIONS
  Intraindividual variation for FT4, FT3 and IGF-1 are low.
authors.affiliation: Department of Chemical Pathology, St Thomas' Hospital, 5th Floor, North Wing, Lambeth Palace Road, London SE1 7EH, UK.
authors.forename: T
authors.initials: T
authors.lastname: Ankrah-Tetteh
authors.forename: S
authors.initials: S
authors.lastname: Wijeratne
authors.forename: R
authors.initials: R
authors.lastname: Swaminathan
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis* / Q000378:metabolism; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood* / Q000378:metabolism; D013963:Thyroid Hormones / Q000097:blood* / Q000378:metabolism
chemical_list: C470125:PTH protein, human; D010281:Parathyroid Hormone; D013963:Thyroid Hormones; D007334:Insulin-Like Growth Factor I