Free insulin-like growth factors -- measurements and relationships to growth hormone secretion and glucose homeostasis

Growth Horm IGF Res. 2004 Oct;14(5):337-75. doi: 10.1016/j.ghir.2004.06.001.


IGF-I is a multipotent growth factor with important actions on normal tissue growth and regeneration. In addition, IGF-I has been suggested to have beneficial effects on glucose homeostasis due to its glucose lowering and insulin sensitizing actions. However, not all effects of IGF-I are considered to be favorable; thus, epidemiological studies suggest that IGF-I is also involved in the development of common cancers, atherosclerosis and type 2 diabetes. The biological actions of IGF-I are modulated by at least six IGF-binding proteins, which bind approximately 99% of the circulating IGF-I pool. So far, most in vivo studies have used serum or plasma total (extractable IGF-I) as an estimate of the bioactivity of IGF-I in vivo. However, within the last decade, validated assays for measurement of free IGF-I have been described. This review aims to discuss the current assays for free IGF-I and their advances in relation to the traditional measurement of total IGF-I. The literature overview will focus on the role of circulating free versus total IGF-I in the feedback regulation of GH release, and the possible involvement of the circulating IGF-system in glucose homeostasis.

Publication types

  • Review

MeSH terms

  • Arteriosclerosis / etiology
  • Blood Glucose / metabolism*
  • Diabetes Mellitus, Type 2 / etiology
  • Homeostasis
  • Human Growth Hormone / metabolism*
  • Humans
  • Insulin-Like Growth Factor Binding Proteins / metabolism
  • Insulin-Like Growth Factor I / analysis*
  • Insulin-Like Growth Factor I / physiology*
  • Neoplasms / etiology


  • Blood Glucose
  • Insulin-Like Growth Factor Binding Proteins
  • Human Growth Hormone
  • Insulin-Like Growth Factor I