title: Serum insulin-like growth factor I reference values for an automated chemiluminescence immunoassay system: results from a multicenter study.
abstract: BACKGROUND
  Analysis of insulin-like growth factor I in serum (S-IGF-I) is an integral component in the diagnosis of GH-related disorders and is going to be of interest in the diagnosis and follow-up of many disorders. The objective of the present study was to develop cross-sectional reference values for S-IGF-I measured by an automated chemiluminescence immunoassay (Nichols Advantage).
  
  
  METHODS
  The study included samples from 3,961 healthy subjects (2,201 males, 1,760 females) aged 1 month to 88 years. Six laboratories were involved in this study and the samples were analyzed by one of seven automated immunoassay systems run in these laboratories. For data analysis, polynomial age and sex-specific models were fitted after transformation of S-IGF-I values.
  
  
  RESULTS
  The results show the well-known age dependency of S-IGF-I levels. At ages <20, higher S-IGF-I levels were seen in girls with an estimated mean peak of 410 microg/l at age 14 and an estimated mean peak of 382 microg/l at age 16 in boys. Thereafter, a rapid decrease was seen to approximately 25 years of age, followed by a slow age-dependent decrease. In adulthood, S-IGF-I in males were slightly, but significantly higher than in females. It could be shown that the mean values of some reference sample subgroups differed significantly from the total mean. However, the multicenter approach used in this study reduces the impact of systematic population, sample handling and laboratory differences on the calculated reference mean.
  
  
  CONCLUSIONS
  The present study establishes age- and sex-specific reference values for a fully automated immunoassay system based on a large population of healthy subjects. The established reference values may be used for this immunoassay system in different laboratories provided that the systematic difference between systems is low.
authors.affiliation: Department of Gastroenterology, Hepatology and Endocrinology, Medizinische Hochschule, Hannover, Germany. brabant.georg@mh-hannover.de
authors.forename: Georg
authors.initials: G
authors.lastname: Brabant
authors.forename: Alexander
authors.initials: A
authors.lastname: von zur Mühlen
authors.forename: Christian
authors.initials: C
authors.lastname: Wüster
authors.forename: Michael B
authors.initials: MB
authors.lastname: Ranke
authors.forename: Jürgen
authors.initials: J
authors.lastname: Kratzsch
authors.forename: Wieland
authors.initials: W
authors.lastname: Kiess
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Ketelslegers
authors.forename: Lars
authors.initials: L
authors.lastname: Wilhelmsen
authors.forename: Lena
authors.initials: L
authors.lastname: Hulthén
authors.forename: Bernhard
authors.initials: B
authors.lastname: Saller
authors.forename: Anders
authors.initials: A
authors.lastname: Mattsson
authors.forename: Jürgen
authors.initials: J
authors.lastname: Wilde
authors.forename: Rudolf
authors.initials: R
authors.lastname: Schemer
authors.forename: Peter
authors.initials: P
authors.lastname: Kann
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007223:Infant; D007231:Infant, Newborn; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D012016:Reference Values
chemical_list: D007334:Insulin-Like Growth Factor I