What is being tested?
Insulin-like growth factor-1 (IGF-1) and growth hormone are hormones that are vital for normal bone and tissue growth and development. GH is produced by the pituitary gland, a grape-sized gland located at the base of the brain behind the bridge of your nose. GH is secreted into the bloodstream in pulses throughout the day and night with peaks that occur mostly during the night. IGF-1 is produced by the liver and to a lesser degree by skeletal muscles, primarily 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. The blood level of IGF-1 mirrors GH levels. However, unlike GH the blood IGF-1 level is stable and does not fluctuate throughout the day.
Like GH, IGF-1 levels are normally low in early childhood, increase gradually during childhood, peak during puberty, and then decline in adult life. Deficiencies in GH and IGF-1 may be caused by conditions such as hypopituitarism or by the presence of a non-GH-producing pituitary tumour that damages hormone-producing cells. Deficiencies in IGF-1 also occur where there is a lack of responsiveness to GH. This insensitivity may be primary (genetic) or secondary to conditions such as malnutrition and chronic diseases. Genetic GH insensitivity (GH resistance) is rare.
Deficiencies early in life can inhibit bone growth and overall development and can result in a child with a short stature. In adults, decreased production can lead to low bone densities, less muscle mass and altered lipids.
Excess GH and IGF-1 can cause abnormal growth of the skeleton and other signs and symptoms characteristic of gigantism and acromegaly. In children, gigantism causes bones to grow longer, resulting in a very tall person with large feet and hands. In adults, acromegaly causes bones to thicken and soft tissues, such as the nose, to swell. Both conditions can lead to enlarged organs, such as the heart, and to other complications such as type 2 diabetes, high blood pressure, increased risk of cardiovascular disease risk, arthritis and a decreased life span. The most common reason for the pituitary to secrete excessive amounts of GH is a GH-producing pituitary tumour (usually benign). Frequently, the tumour can be surgically removed and/or treated with drugs or radiation. In most cases, this will cause GH and IGF-1 levels to return to normal or near normal levels.
How is it used?
A test for insulin-like growth factor-1 (IGF-1) may be used to help:
IGF-1 may be ordered with other pituitary hormone tests, such as adrenocorticotropic hormone (ACTH), to help diagnose hypopituitarism. It may be used to monitor the effectiveness of treatment for GH deficiencies and GH insensitivity.
IGF-1 testing and a GH suppression test can be used to detect a GH-producing pituitary tumour. Its presence is then confirmed with imaging scans that help identify and locate the tumour. If surgery is necessary, GH and IGF-1 levels are measured after the tumour’s removal to determine whether or not all of it was successfully removed. Drug and/or radiation therapy may be used in addition to (or sometimes instead of) surgery to try to decrease GH production and return IGF-1 to normal or near normal concentrations. IGF-1 may be used to monitor the effectiveness of this therapy at regular intervals for years afterward to monitor GH production and to detect tumour recurrence.
When is it requested?
Insulin-like growth factor-1 (IGF-1) testing may be ordered, along with a GH stimulation test when a child has symptoms of GH deficiency, such as a slowed growth rate and short stature. They also may be ordered when adults have symptoms that the doctor suspects may be due to a GH deficiency. An IGF-1 also may be ordered when a doctor suspects that a person has an underactive pituitary gland and at intervals to monitor patients on GH therapy.
IGF-1 testing may be ordered, along with a GH suppression test, when a child has symptoms of gigantism, an adult shows signs of acromegaly.
When a GH-producing pituitary tumour is found, GH and IGF-1 are ordered after the tumour is surgically removed to determine whether all of the tumour has been extracted. IGF-1 also is ordered at regular intervals when a patient is receiving drug and/or radiation therapy that frequently follow tumor surgery.
IGF-1 levels may be ordered at regular intervals for many years to monitor a patient’s GH production and to watch for pituitary tumour recurrence.
What does the result mean?
Normal concentrations of Insulin-like growth factor-1 (IGF-1) must be considered in context. Some patients can have a growth hormone (GH) deficiency and still have a normal IGF-1 concentration.
Decreased IGF-1
If IGF-1 concentrations are decreased, then it is likely that there is GH deficiency or an insensitivity to GH. If this is in a child, the GH deficiency may have already caused short stature and delayed development and may be treated with GH supplementation. Adults will have an age-related decrease in production, but lower than expected concentrations may reflect a GH deficiency or insensitivity.
If a decrease in IGF-1 is due to a more general decrease in pituitary function (hypopituitarism), then several of the patient’s pituitary hormones will need to be evaluated and may be supplemented to bring them up to normal levels. Reduced pituitary function may be due to inherited defects or can rise as a result of pituitary damage following conditions such as trauma, infections and inflammation.
Decreased levels of IGF-1 also may be seen with nutritional deficiencies (including anorexia nervosa), chronic kidney or liver disease, and with high doses of oestrogen.
Increased IGF-1
Elevated levels of IGF-1 usually indicate an increased production of GH. Increased concentrations of IGF-1 are most commonly due to pituitary tumours.
If IGF-1 is still elevated after the surgical removal of a pituitary tumour, then the surgery may not have been fully effective. Decreasing IGF-1 concentrations during subsequent drug and/or radiation therapies indicate that the treatment is lowering GH production. If levels of IGF-1 become ‘normalised,’ then the patient is no longer producing excess amounts of GH. When a patient is undergoing long term monitoring, an increase in IGF-1 levels may indicate a recurrence of the pituitary tumour.
Is there anything else I should know?
If an IGF-1 level is normal and the doctor still strongly suspects a GH deficiency, then he may order another test, such as an IGF BP 3 (insulin-like growth factor binding protein 3), and/or GH stimulation test.
Common questions
In children, the following may indicate GH and/or IGF-1 deficiency:
In adults, abnormally low levels of GH and/or IGF-1 may cause subtle, nonspecific symptoms such as:
As long as you are considered to have abnormal (low or high) GH production or are receiving treatment for one of the conditions your IGF-1 will need to be monitored.
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