Insulin-like growth factor binding protein-3 (IGFBP-3)

IGFBP-3 is produced largely by the liver but to a lesser extent in fibroblasts, the ovaries, and the placenta. The Insulin like growth factor binding proteins bind IGF-I and IGF-II with high affinity and control the ability of IGF-1 and IGF-II to bind to their receptors. The major functions of the IGF-binding proteins in circulation are:

a) to transport IGFs in the vascular system,
b) to regulate their half-lives, and
c) to control transcapillary transport into the extravascular fluid compartments.

IGFBP-3 is the predominant IGF carrier of six distinct IGF binding proteins structurally characterised. It is responsible for complexing and transporting approximately 95% of circulating IGF-I and IGF-II.

Similarly to age-related changes for IGF-I, serum IGFBP-3 concentrations vary with age. In growth hormone deficient children, IGFBP-3 concentrations increase following GH administration whilst in contrast IGFBP-2 decreases following administration. Measurement of the binding proteins is useful in discriminating between growth hormone deficiency and short stature due to other aetiologies in children. IGFBP-3 may also be low in patients with short stature due to poorly controlled diabetes. In addition, IGFBP-3 decreases in calorific and protein restriction therefore IGFBP-3 measurement offers a useful tool in assessing nutritional status.