Growth hormone (GH) is secreted by the anterior pituitary gland in a pulsatile pattern — primarily during deep sleep and exercise. It stimulates growth in children and adolescents, and in adults it continues to regulate body composition, metabolism, bone density, and cardiac function. GH acts directly on tissues and also stimulates the liver to produce IGF-1, which mediates many of its growth-promoting effects.

GH testing is used to investigate both excess and deficiency. In children, GH deficiency causes short stature; in adults, it causes fatigue, reduced muscle mass, increased fat mass, and poor quality of life. Excess GH — typically from a pituitary tumour — causes acromegaly in adults (enlarged hands, feet, and facial features) and gigantism in children. A single GH measurement is rarely diagnostic due to its pulsatile nature; IGF-1 is often used as a more stable surrogate.