IGF Binding Protein-3 (IGFBP-3) - Insulin-like growth factor binding proteins bind IGF-I and IGF-II with high affinity but do not bind insulin. Of the 6 distinct IGF binding proteins structurally characterized at this time, IGFBP-3 has been shown to be the major carrier of the IGFs, transporting approximately 95% of circulating IGF-I and IGF-II. IGFBP-3 is growth hormone (GH) responsive. Thus, levels are high in acromegaly and low in hypopituitarism, and levels increase in GH-deficient children after GH administration. Other causes of short stature that result in reduced IGFBP-3 levels include poorly controlled diabetes. The IGFBP-3 assay is useful in assessing nutritional status, since IGFBP-3 decreases during both caloric and protein restriction.
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