Insulin-like Growth Factor 1 (IGF-1)

The Insulin-like Growth Factor 1 (IGF-1; Somatomedin C) assay is used to assess growth disorders across the lifespan and to evaluate pituitary function. Persistently elevated IGF-1 supports a diagnosis of GH excess—gigantism in children or acromegaly in adults—and is used in conjunction with GH suppression testing. IGF-1 also assists with postoperative assessment and long-term surveillance after resection of GH-secreting pituitary adenomas, and during adjuvant medical or radiation therapy. IGF-1 measurement can be used to track response to GH therapy and, when integrated with clinical and other laboratory data, may help identify GH resistance.

Compared with single measurements of growth hormone (GH), IGF-1 provides a more reliable reflection of endogenous GH secretion because GH is released in pulses while IGF-1 is relatively stable. IGF-1 is produced in the liver, skeletal muscle, and other tissues in response to GH and mediates many of GH’s effects on skeletal and soft-tissue growth and body composition. Circulating concentrations are low in early childhood, rise to a pubertal peak, and then decline through adulthood. Low IGF-1 may be due to hypopituitarism or to GH insensitivity associated with conditions such as hypothyroidism, sex steroid deficiency, or chronic systemic illness; genetic forms of GH resistance are uncommon. Excess GH with elevated IGF-1 leads to gigantism in children and acromegaly in adults, characterized by skeletal overgrowth, soft-tissue expansion, cardiometabolic complications, and shortened longevity; the usual etiology is a pituitary adenoma, and effective medical, surgical, or radiation therapy generally normalizes IGF-1. IGF-1 concentrations do not differentiate pituitary dwarfism from constitutional delay of growth and development.