IGF 1, also called somatomedin C, is a protein produced by the liver, muscles and other tissues in response to growth hormone (GH) stimulation. IGF 1 promotes the growth of bone and muscle mass. Unlike GH, IGF 1 secretion is constant throughout the day. This means that blood levels of IGF 1 are an excellent reflection of GH secretion by the pituitary gland. Results are expressed in micrograms of IGF 1 per litre (µg/L), and the indicated reference values are based on the age and sex of the individual.
Normal levels of IGF 1 must be interpreted in context, as some individuals have normal levels of IGF 1 despite a GH deficiency. Low levels of IGF 1 usually indicate a GH deficiency or resistance to GH action. Low levels may also be caused by malnutrition (e.g., anorexia) or chronic kidney or liver disease.
High levels of IGF 1 generally indicate the presence of a pituitary tumour. IGF 1 levels are also high during growth and pregnancy. The presence of a GH-producing tumour may decrease the secretion of one or more other pituitary hormones (TSH, FSH, LH, prolactin, ACTH).