The Insulin-Like Growth Factor-I (IGF-I) test is a blood test used to measure the level of IGF-I in a person’s blood. IGF-I is a hormone produced by the liver and other tissues in response to the growth hormone (GH) released by the pituitary gland. IGF-I plays a critical role in regulating growth and development, particularly during childhood and adolescence, and also has important functions in metabolism and tissue repair in adults. The IGF-I test is used to diagnose and monitor certain conditions related to GH deficiency, such as growth hormone deficiency (GHD), Turner syndrome, and chronic renal insufficiency. Additionally, the test can be used to evaluate the effectiveness of GH replacement therapy and to assess the risk of certain diseases, such as acromegaly and some types of cancer, which can result from excess GH or IGF-I production.