title: Insulin-like growth factor I: pros and cons of a bioassay.
abstract: BACKGROUND
  Insulin-like growth factor I (IGF-I) immunoassays are primarily used to estimate IGF-I status. Recently an IGF-I-specific kinase receptor activation assay (KIRA) was developed as an alternative method for measuring IGF-I bioactivity. When compared with IGF-I immunoassays, the IGF-I KIRA has the theoretical advantage of measuring the net effects of IGF-binding proteins on IGF-I receptor activation. The IGF-I KIRA is sensitive and specific and has, for a bioassay, a very low intra- and inter-assay coefficient of variation (<7 and <15%, respectively). Several studies have shown that the IGF-I KIRA is more sensitive than IGF-I immunoassays for detecting differences in clinical state. In addition, the IGF-I KIRA seems superior to IGF-I immunoassays for monitoring acute effects of therapeutic interventions.
  
  
  CONCLUSIONS
  It is not known if IGF-I KIRA is superior to IGF-I immunoassays for evaluating the efficacy of growth hormone (GH) treatment for GH deficiency and of GH receptor antagonist treatment for acromegaly. However, IGF-I KIRA undoubtedly will provide new insights into the factors that regulate IGF-I bioactivity in the circulation in both healthy and diseased states.
authors.affiliation: Department of Internal Medicine, Erasmus Medical Center, Rotterdam, The Netherlands. j.a.m.j.l.janssen@erasmusmc.nl
authors.forename: J A M J L
authors.initials: JA
authors.lastname: Janssen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001681:Biological Assay / Q000379:methods*; D002460:Cell Line; D006801:Humans; D007118:Immunoassay; D018969:Insulin-Like Growth Factor Binding Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008297:Male; D010766:Phosphorylation; D017526:Receptor, IGF Type 1 / Q000378:metabolism
chemical_list: D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1