The Insulin-Like Growth Factor I (IGF-I) blood test is used to measure IGF-I levels, a hormone that plays a key role in regulating cell growth and development. This hormone is mainly secreted by the liver in response to growth hormone and serves as an important indicator of endocrine health. The test is used to assess growth delays in children and to diagnose and monitor certain hormonal disorders, such as pituitary gland insufficiency. It can also be used in some cases to monitor cancer progression. The results help doctors understand the patient’s health status and guide appropriate treatment plans.