Along with growth hormone (GH), the hormone insulin-like growth factor-1 (IGF-1) aids in the correct growth and development of bones and other tissues. IGF-1 levels in the blood are determined by the test. In response to GH stimulation, IGF-1 is principally produced by the liver, skeletal muscles, and numerous other tissues. Many of the effects of GH are mediated by IGF-1, which also encourages bone and other tissue growth and lean muscle mass synthesis. IGF-1 has been linked to metabolic syndrome and is also involved in non-growth processes like glucose and lipid metabolism.