Free insulin-like growth factor I serum levels in 1430 healthy children and adults, and its diagnostic value in patients suspected of growth hormone deficiency.

Serum levels of total insulin-like growth factor I (IGF-I) and IGF-binding protein-3 (IGFBP-3) reflect endogenous GH secretion in healthy children, which makes them good diagnostic markers for screening of GH deficiency (GHD) in short children, although some controversy still exists. Only a minor fraction of the total IGF-I circulates in its free form, which is believed to be the biologically active form. However, our knowledge of the clinical or physiological value of determination of free IGF-I in serum is limited at present. In adults, the diagnostic value of total IGF-I and IGFBP-3 determinations in patients suspected of GHD has only been reported in a few studies, whereas no previous reports on the diagnostic value of free IGF-I levels in adults suspected of GHD exist. Serum levels of free IGF-I were determined in 1430 healthy children, adolescents, and adults by a newly developed, commercially available immunoradiometric assay (Diagnostic Systems Laboratories) to establish valid normative data for t...