IGF-1 test: what it measures and results

IGF-1 is a protein hormone, most of which is produced by the liver in response to growth hormone (GH) released by the pituitary gland. It carries the effect of growth hormone to cells — it stimulates the growth of bone, cartilage and other tissues, and takes part in metabolism. Unlike growth hormone, whose level in the blood changes abruptly, in short pulses through the day, the concentration of IGF-1 stays fairly steady, so it better reflects the average activity of growth hormone over a longer period. Because of this, the IGF-1 test is used as an indirect indicator of growth hormone status: it is used to investigate growth disorders in children, growth hormone deficiency or excess in adults, and to monitor the effect of treatment. The amount of IGF-1 depends on age (it is highest in adolescence), sex, nutrition and liver function, so the result is always assessed together with other tests and the clinical picture.

• In children, when growth has slowed or height lags markedly behind that of children of the same age — when growth hormone deficiency is suspected
• When resistance to growth hormone (Laron syndrome) or another inherited growth disorder is suspected
• In adults, when growth hormone deficiency is suspected — because of tiredness, reduced muscle and bone mass
• In children, when unusually rapid growth is noticed — when gigantism is suspected
• In adults, when signs of acromegaly are noticed — enlarged hands, feet and facial features, a thickened voice
• To monitor the course of treatment of an already diagnosed growth hormone disorder

This page gives no numeric reference interval for IGF-1. The interval depends on the laboratory's method, so you will find the exact reference interval of your own laboratory on your result report — it is printed together with the result. The amount of IGF-1 depends on age (it is highest in adolescence), sex, nutrition and liver function, so the result is always assessed together with other tests and the clinical picture. A single result rarely gives the full picture: the doctor assesses it together with growth hormone tests, clinical signs and, if needed, imaging tests of the pituitary gland.

A raised IGF-1 result

A raised IGF-1 most often indicates an excess of growth hormone — in children this can mean gigantism, in adults acromegaly. The main cause is a pituitary tumour producing too much growth hormone. Treatment options include radiotherapy, surgery or medicines — this is decided by the doctor according to the cause.

Causes of a raised result

• A tumour affecting the pituitary gland that produces too much growth hormone
• If the cause is not a tumour, further tests may be needed to establish the cause more precisely

Signs of a raised IGF-1

• Unusually rapid growth in children
• Enlarged hands and feet
• Coarsened facial features
• A thickened (hoarse) voice
• Increased sweating
• Thickened bones
• A disturbed menstrual cycle

What is usually assessed after a raised result

• Imaging tests of the pituitary gland (MRI), if a tumour is suspected
• A growth hormone test and a suppression test for a more precise assessment
• An assessment of vision, if the tumour may be pressing on the optic nerves
• A discussion of treatment options with an endocrinologist

A low IGF-1 most often indicates a growth hormone deficiency or resistance to it. In children this can slow growth; in adults it can reduce muscle and bone mass and cause tiredness. The cause may be genetic, related to a disease of the brain, or the natural age-related decline in the level.

Causes of a low result

• Genetic disorders of growth hormone deficiency or of resistance to it (for example, Laron syndrome)
• A disease of the brain (the pituitary gland) that disrupts the production of growth hormone
• The natural age-related decline in the amount of IGF-1

Signs of a low IGF-1

• Slowed growth and short height in children
• Small sex glands in boys
• Thinner hair and poor nail growth in children
• Tiredness in adults
• Reduced muscle and bone mass in adults

What is usually assessed after a low result

• A growth hormone stimulation test for a more precise assessment
• In children — an assessment of the growth chart and of bone age
• A discussion with an endocrinologist about possible treatment with growth hormone, especially in children
• A check of the other pituitary hormones, if a broader problem of pituitary function is suspected

Related pages

IGF-1 is more stable in the blood than growth hormone itself, so the two are often looked at together: see growth hormone. Other pituitary and hormone tests explained in English on this site: ACTH, cortisol, TSH and parathyroid hormone. See also how to read blood test results and how to prepare for a blood test.