IGF-1 (Insulin-like Growth Factor 1) is a hormone produced mainly by the liver in response to growth hormone (GH) stimulation. This version of the test measures IGF-1 using liquid chromatography-mass spectrometry (LC/MS), a highly specific and precise laboratory method. Because IGF-1 levels remain relatively stable throughout the day, the test is often used as an indirect indicator of average growth hormone activity. This test is commonly used to help evaluate conditions related to growth hormone production, including growth hormone deficiency and excess (such as acromegaly or gigantism). It may be used to assess unexplained growth problems in children, to help investigate pituitary gland disorders, and to monitor treatment in people receiving therapy for growth hormone-related conditions. Results are interpreted alongside other tests and clinical information by a healthcare provider.