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IGF-1 is the precise test for human growth hormone activity. It is synthesized in the liver upon stimulation of the pituitary human growth hormone (HGH). Actually HGH is a misnomer. It is also called Somatomedin-C (Sm-C). Clinical studies have shown that HGH administration to the elderly has significantly increased IGF-1 and has had marvelous rejuvenating effects. Some of these are improved cognizance, muscle and bone strength, libido enhancement, and athletic performance.
IGF-1 (Somatomedin-C) is a polypeptide hormone produced mostly by the liver, with effect on growth promoting activity and glucose metabolism (insulin-like activity). Somatomedin-C is carried in blood bound to a carrier protein which prolongs its half-life. Its level is therefore more constant than that of HGH.
Traditionally, IGF-1 is used to diagnose acromegaly, where IGF-1 and HGH are increased; evaluate hypopituitarism and hypothalamic lesions in children (diagnosis of dwarfism and response to therapy). Low levels occur in Laron dwarfism, an entity in which HGH is increased. Most recently HGH injections are used by some doctors to increase IGF-1 levels in elderly patients for rejuvenation.
Malnutrition can cause low Somatomedin-C levels in spite of normal amounts of circulating HGH. The Sm-C level does not distinguish pituitary dwarfism from constitutional delay of growth and development.
Low values are described with the extremes of age (first 5-6 years and advanced age), hypopituitarism, malnutrition, diabetes mellitus, Laron dwarfism, hypothyroidism, maternal deprivation syndrome, pubertal delay, cirrhosis, hepatoma, and some cases of short stature and normal GH response to pharmacological tests. Low values may be found with nonfunctioning pituitary tumors, with constitutional delay of growth and development and with anorexia nervosa.
High values occur with adolescence, true precocious puberty, pregnancy, obesity, pituitary gigantism, acromegaly and diabetic retinopathy.
Since Sm-C is decreased with malnutrition, its concentration provides an index with which to monitor therapy for food deprivation.
High levels of IGF-1 have been implicated in cancers of the prostate and breast. However, these findings have not been substantiated.
Values obtained with different assay methods should not be used interchangeably.