Growth Hormone (GH) is a pituitary hormone that plays a crucial role in growth, metabolism, and body composition throughout life. This test measures GH levels in the blood to evaluate pituitary function and diagnose disorders related to GH deficiency or excess. GH stimulates the liver to produce insulin-like growth factor-1 (IGF-1), which promotes growth of bones and tissues. In children, GH deficiency can cause short stature and delayed growth, while excess GH can lead to gigantism. In adults, GH deficiency may cause decreased muscle mass, increased body fat, and reduced bone density, while excess GH can result in acromegaly (enlargement of bones and soft tissues). GH secretion is episodic and follows a daily rhythm, so single measurements may not be reliable. This test is typically used in conjunction with stimulation or suppression tests to evaluate pituitary function and diagnose conditions affecting growth and metabolism.