Insulin-like Growth Factor-binding Protein 3 (IGFBP-3)

The IGFBP-3 (IGF-binding protein 3) test assesses the somatotropic axis because production is largely growth hormone dependent and circulating levels are more stable than pulsatile GH. Measurement is used in the evaluation of pediatric short stature and suspected GH deficiency, hypopituitarism, acromegaly and gigantism, and suspected GH insensitivity. IGFBP-3, interpreted together with IGF-1, is used to monitor recombinant growth hormone therapy and to follow patients with GH-secreting pituitary adenomas after surgery and over time, including during and after adjuvant medical therapy or radiotherapy.

In circulation, IGFBP-3 binds IGF-I and IGF-II, most commonly as a ternary complex with the acid-labile subunit, which modulates IGF bioactivity and prolongs half-life. Concentrations change with age: values rise through early childhood, peak during puberty, and then decline modestly in adult life. Nutritional status and hepatic and renal function affect results. Levels decrease with fasting, chronic malnutrition, hepatic failure, and diabetes mellitus, and increase in chronic renal failure. Because IGFBP-3 synthesis is growth hormone dependent and shows less short-term variability than GH itself, measurement provides adjunctive information for the assessment of GH deficiency and excess and for monitoring GH-targeted therapies.