Insulin-like growth factors (IGF-I, IGF-II) are a family of peptides involved in the regulation of cell growth, the actions of which are mediated by binding to the insulin-like growth factor binding proteins. Six binding proteins (IGFBP-1 through IGFBP-6) have been described. IGFBP-3 is the most predominant of these. IGFBP-3 is a 264-amino acid peptide (MW 29kD) which forms a 150kD glycoprotein complex consisting of IGFBP-3 itself and an IGF molecule. Approximately 95% of IGF-I and IGF-II are bound to IGFBP-3, which makes this protein the major carrier of the insulin-like growth factors in circulation. The function of the binding protein is to extend the half-life of the growth factors in the circulation, to several hours.
IGFBP-3 is used as an aid in the evaluation of growth disorders. It is growth hormone (GH) dependent and therefore useful in the evaluation of GH secretion.