Insulin-like growth factor 1 (IGF-1) is a hormone that manages the effects of growth hormone (GH) in the body. Together, IGF-1 and GH promote normal growth of bones and tissues. IGF-1 is primarily produced in the liver, skeletal muscles, and many other tissues in response to GH stimulation. IGF-1 mediates many of the actions of GH, stimulates the growth of bones and other tissues, and promotes the production of lean muscle mass. IGF-1 also plays a role in non-growth activities, such as glucose and lipid metabolism, and has been implicated in metabolic syndrome. An IGF-1 test measures the amount of IGF-1 in the blood and is used to diagnose growth hormone disorders. If a persons IGF-1 levels are lower than normal, it may indicate a GH deficiency or insensitivity to GH. If IGF-1 levels are higher than normal, it may indicate gigantism in children or acromegaly in adults.