Clinical utility of insulin-like growth factor assays.

Insulin-like growth I and II (IGF-I and II) mediate many of the peripheral mitogenic actions of growth hormone (GH). The marked dependence of IGF levels on GH adequacy has led to the development of commercial immunoassays for IGF-I (somatomedin-C), and the widespread use of IGF-I levels in the evaluation of short stature. Proper interpretation of IGF-I levels requires consideration of assay methodology, age-related norms, clinical findings, nutritional status, and concurrent hormonal and disease processes. IGF-I levels alone cannot be used to predict stimulated GH response, but may have value in directing the clinical evaluation of a child with short stature. Low IGF-I levels may also be characteristic of a subpopulation of short children with neurosecretory GH deficiency. The role of IGF-II levels in the evaluation of short stature is uncertain, although the combination of low IGF-I and IGF-II levels is more specific for GH deficiency than either value alone. Other clinical applications for IGF assays in pediatrics are also reviewed.