Insulin-like growth factor 1 (IGF-1) is a hormone produced primarily by the liver in response to growth hormone (GH) stimulation from the pituitary gland. While GH itself is released in short pulses, mainly during deep sleep, IGF-1 circulates at relatively stable levels throughout the day. This stability is what makes IGF-1 the more practical and reliable marker for assessing growth hormone status in clinical practice.
IGF-1 mediates many of the effects attributed to growth hormone, including promoting bone and muscle growth during childhood, and maintaining body composition, bone density, and metabolic function in adults. Levels peak during adolescence, when growth is most rapid, and decline progressively with age. Because of this age-dependent pattern, results must always be compared against age-specific and sex-specific reference ranges.
Low IGF-1 in the appropriate clinical context suggests growth hormone deficiency. In children, this may present as short stature and delayed growth velocity. In adults, GH deficiency following pituitary damage (from tumours, surgery, radiation, or head injury) can cause increased body fat, reduced lean muscle, low energy, and poor bone density. Low IGF-1 can also result from malnutrition, liver disease, hypothyroidism, and poorly controlled diabetes, so these factors are considered during interpretation.
Elevated IGF-1 raises the possibility of growth hormone excess. In adults, persistent GH overproduction, usually from a benign pituitary tumour, leads to acromegaly. In children, the equivalent condition is gigantism. IGF-1 is also used to monitor treatment response in people receiving growth hormone therapy.
Because a single IGF-1 result provides meaningful information but is rarely conclusive on its own, your practitioner will interpret it alongside clinical findings and may recommend further dynamic testing if the result is abnormal.
To screen for growth hormone deficiency or excess, investigate growth disorders in children, evaluate pituitary function, and monitor growth hormone replacement therapy.
