Also known as: Somatomedin C
Name: Insulin-like growth factor 1
Related tests: Glucose, Growth hormone
Why get tested?
To identify diseases and conditions caused by a lack or overproduction of growth hormone (GH), to assess pituitary function and to monitor the effectiveness of GH treatment
When to get tested?
As part of an assessment of pituitary function; when there are symptoms such as slow growth, short stature and delayed development (in children) or reduced bone density, reduced muscle strength and raised lipids (in adults) that suggest insufficient GH and IGF-1 production; when there are symptoms of gigantism in children or acromegaly in adults that suggest excess GH and IGF-1 production; during and after treatment for GH abnormalities
Sample required?
A blood sample taken from a vein in the arm, or from a finger-prick in children
What is being tested?
The IGF-1 test is an indirect measure of the average amount of growth hormone (GH) produced by the body. IGF-1 and GH are peptide hormones, small proteins that are vital for the normal development and growth of bones and tissues. GH is produced by the pituitary gland, a grape-sized gland located at the base of the skull in the sella turcica of the sphenoid bone. GH is released into the bloodstream in pulses during the day and night, peaking mainly at night. IGF-1 is produced by the liver and, to a lesser extent, by skeletal muscle, mainly in response to GH stimulation. It mediates many of the actions of GH, stimulating the growth of bones and other tissues and promoting the production of lean muscle mass. IGF-1 reflects excesses and deficiencies of GH, but its level is stable during the day, which makes it a useful indicator of average GH levels.
As with GH, average IGF-1 levels are normally low in early childhood, rise gradually in adolescence, peak during puberty and then decline in adulthood. GH and IGF-1 deficiencies can be caused by conditions such as hypopituitarism or by a pituitary tumour that does not produce GH and damages the hormone-producing cells. IGF-1 deficiency also occurs when there is a lack of response to GH. This insensitivity can be primary (genetic) or secondary to conditions such as malnutrition and chronic diseases.
Deficiencies in the first years of life can inhibit bone growth and development in general and can result in a child being shorter than normal. In adults, reduced production can lead to low bone density, reduced muscle mass and abnormal lipids.
Excess GH and IGF-1 can cause abnormal growth of the skeleton and other signs and symptoms typical of gigantism and acromegaly. In children, gigantism causes the long bones to grow, resulting in a very tall person with large hands and feet. In adults, acromegaly causes thickening of the bones and swelling of soft tissues, e.g. the nose. Both conditions can lead to enlarged organs, such as the heart, and other complications such as type 2 diabetes, an increased risk of cardiovascular disease, high blood pressure, arthritis and a shorter life expectancy. The most common reason for the pituitary gland to release too much GH is a GH-producing pituitary tumour (usually benign). The tumour can often be removed surgically and/or treated with medicines or radiotherapy. In most cases this brings GH and IGF-1 back to normal or near-normal levels.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm or by pricking a child’s finger.
Is any preparation needed to ensure the quality of the sample?
Generally no preparation is needed; however, since the test may be done at the same time as others, fasting for at least 12 hours may be required
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
IGF-1 is measured to help diagnose the cause of growth abnormalities and to assess pituitary function. It is not used to diagnose GH deficiency on its own, but may be requested together with GH stimulation tests to provide further information. IGF-1 levels and GH measurement can also provide information on GH insensitivity.
IGF-1 may be requested together with tests of other pituitary hormones, such as adrenocorticotrophic hormone (ACTH), to help diagnose hypopituitarism. It can be used to monitor the effectiveness of treatment for growth hormone deficiency and insensitivity.
IGF-1 and a GH suppression test can be used to detect a GH-producing pituitary tumour. Its presence is then confirmed by imaging scans, which help identify and locate the tumour. If surgery is needed, GH and IGF-1 levels are measured after the tumour has been removed to determine whether removal was successful. Medicines or radiotherapy may be used in addition to surgery, or sometimes instead of it, to try to reduce GH production and bring IGF-1 back to normal or near-normal concentrations. IGF-1 can be used to monitor the effectiveness of this treatment at regular intervals for years afterwards, to check GH production and detect recurrence of the tumour.
When is it requested?
IGF-1 may be requested, together with a GH stimulation test, when a child has symptoms of GH deficiency, such as slow growth and short stature. Both tests may also be requested when adults have symptoms that the doctor suspects may be due to GH deficiency. IGF-1 may also be requested when the doctor suspects that a person has an underactive pituitary gland, and periodically to monitor patients on GH treatment.
IGF-1 may be requested, together with GH suppression tests, when a child has symptoms of gigantism, an adult shows signs of acromegaly, and/or when the doctor suspects that a patient has hyperpituitarism.
When a GH-producing pituitary tumour is found, GH and IGF-1 tests are requested after the tumour has been surgically removed to determine whether all of it has been removed. IGF-1 is also requested at regular intervals when a patient is being treated with medicines or radiotherapy, as often happens after tumour surgery.
IGF-1 levels may be checked periodically for years to monitor a patient’s GH production and to look for recurrence of the pituitary tumour.
What does the test result mean?
Normal IGF-1 concentrations must be considered in context. Some patients may have GH deficiency and a normal IGF-1 concentration.
If IGF-1 concentrations are low, there is probably GH deficiency (GHD) or a lack of response to GH. If this occurs in a child, GH deficiency may already have caused short stature and delayed development and can be treated with GH supplements. Adults will have an age-related decline in production, but lower than expected concentrations may reflect GH deficiency or insensitivity
If a fall in IGF-1 is due to a more general decline in pituitary function (hypopituitarism), several of the patient’s pituitary hormones will need to be assessed and may need to be replaced to bring them to normal levels. Reduced pituitary function can be caused by inherited defects or can result from damage to the pituitary gland due to injury, infection or inflammation.
Low IGF-1 levels can also occur with nutritional deficiencies (including anorexia nervosa), chronic kidney or liver disease, inactive or ineffective forms of GH, and high doses of oestrogen.
High IGF-1 levels usually indicate increased GH production. Since GH levels vary during the day, IGF-1 concentrations reflect average GH production, not the actual amount of GH in the blood. This holds true up to the point at which the liver’s capacity to produce IGF-1 is reached. With very high GH production, IGF-1 levels will level off at a high maximum concentration.
Increased GH and IGF-1 concentrations are normal during puberty and pregnancy, but otherwise are very often due to pituitary tumours, which are usually benign. If other pituitary hormones are also abnormal, the patient may have a condition causing generalised hyperpituitarism.
If IGF-1 is still high after surgical removal of a pituitary tumour, the operation may not have been fully effective. Falling IGF-1 concentrations during subsequent drug treatment and/or radiotherapy indicate that the treatment is lowering GH production. If IGF-1 levels “normalise”, the patient is no longer producing excess GH. When a patient is monitored long term, rising IGF-1 levels may indicate recurrence of the pituitary tumour.
Is there anything else I should know?
If IGF-1 is normal and the doctor still strongly suspects GH deficiency, they may request another test, IGFBP-2 or IGFBP-3 (insulin-like growth factor binding protein 2 or 3), to help confirm GH deficiency
1. What signs and symptoms are seen with GH and IGF-1 deficiency?
2. What signs and symptoms are seen with excess GH and IGF-1 production?
3. How long do I need to be monitored?
1. What signs and symptoms are seen with GH and IGF-1 deficiency?
In children, the following signs may indicate GH and/or IGF-1 deficiency:
• slower growth in early childhood compared with the norm for the age group
• shorter stature than their peers
• delayed puberty
• X-rays showing delayed bone development.
In adults, abnormally low GH and/or IGF-1 levels can cause subtle, non-specific symptoms such as:
• reduced bone density
• tiredness
• harmful lipid changes
• reduced exercise tolerance.
2. What signs and symptoms are seen with excess GH and IGF-1 production?
In a child, the first thing noticed is unusual height. In adults, the changes may be less obvious: a larger nose, thicker lips, a more prominent jaw, rings and shoes that no longer fit. Other signs and symptoms can include:
• a deeper, hoarse voice
• enlarged organs: liver, heart, kidneys and spleen
• an enlarged tongue (macroglossia)
• erectile dysfunction
• tiredness
• headache and visual disturbances
• joint pain and swelling
• irregular periods
• muscle weakness
• snoring
• sweating and excessive perspiration
• thickening of the skin
• trapped nerves (carpal tunnel syndrome)
3. How long do I need to be monitored?
For as long as you have abnormal (low or high) GH production or are on GH replacement therapy, your IGF-1 will need to be checked.