At a glance

Also known as

Somatomedin C

Why get tested?

To identify diseases and conditions caused by deficiencies and overproduction of growth hormone (GH), to evaluate pituitary function, and to monitor the effectiveness of GH treatment

When to get tested?

As part of an evaluation of pituitary function; when you have symptoms of slow growth, short stature, and delayed development (in children) or decreased bone density, reduced muscle strength and increased lipids (in adults) that suggest insufficient GH and IGF-1 production; when you have 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 drawn from a vein in your arm or by a fingerstick (in children)

Test preparation needed?

None, unless instructed to fast

What is being tested?

The insulin-like growth factor-1 (IGF-1) test is an indirect measure of the average amount of growth hormone (GH) being produced by the body. IGF-1 and GH are peptide hormones, small proteins 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. IGF-1 mirrors GH excesses and deficiencies, but its level is stable throughout the day, making it a useful indicator of average GH levels.

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.

Deficiencies early in life can inhibit bone growth and overall development and can result in a child with a shorter than normal 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, increased cardiovascular disease risk, high blood pressure, 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 the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in your arm or by a fingerstick (in children).

Is any test preparation needed to ensure the quality of the sample?

In general, no test preparation is needed; however, since this test may be performed at the same time as others, fasting for at least 12 hours may be required.

The Test

How is it used?

IGF-1 is measured to help diagnose the cause of growth abnormalities and to evaluate pituitary function. It is not diagnostic of GH deficiency but may be ordered along with GH stimulation tests to offer additional information. IGF-1 levels and the measurement of GH can also provide information related to GH insensitivity.

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 growth hormone deficiencies and growth hormone 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?

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, and/or when a doctor suspects that a patient has hyperpituitarism.

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 undergoing the 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 test result mean?

Looking for reference ranges?

Normal concentrations of IGF-1 must be considered in context. Some patients can have a 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 a deficiency of GH (GH deficiency; GHD) 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, inactive/ineffective forms of GH, and with high doses of oestrogen.

Increased IGF-1
Elevated levels of IGF-1 usually indicate an increased production of GH. Since GH levels vary throughout the day, IGF-1 concentrations are a reflection of average GH production, not of the actual amount of GH in the blood. This is accurate up to the point at which the liver’s capacity to produce IGF-1 is reached. With severely increased GH production, IGF-1 levels will stabilise at an elevated maximum concentration.

Increased concentrations of GH and IGF-1 are normal during puberty and pregnancy but otherwise are most frequently due to pituitary tumours (usually benign). If other pituitary hormones are also abnormal, then the patient may have a condition causing general hyperpituitarism.

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, an IGF BP 2 or IGF BP 3 (insulin-like growth factor binding protein 2 or 3), to help confirm the GH deficiency.

Common Questions

What signs and symptoms are seen with deficient GH and IGF-1?

In children, the following may indicate GH and/or IGF-1 deficiency:
  • Slowed growth rate in early childhood relative to group norms
  • Shorter stature than others of the same chronological age
  • Delayed puberty
  • X-rays showing delayed bone development.

In adults, abnormally low levels of GH and/or IGF-1 may cause subtle, nonspecific symptoms such as:

  • Decreased bone density
  • Fatigue
  • Adverse lipid changes
  • Reduced exercise tolerance.

What signs and symptoms are seen with excess GH and IGF-1 production?

In a child, it is unusual tallness that is often first noticed. With an adult, it may be more subtle: a larger nose, thicker lips, a more prominent jaw or rings and shoes that no longer fit. Other signs and symptoms may include:
  • Deepened, husky voice
  • Enlarged organs - liver, heart, kidneys and spleen
  • Enlarged tongue
  • Erectile dysfunction
  • Fatigue
  • Headaches and visual disturbances
  • Joint pain and swelling
  • Menstrual cycle irregularities
  • Muscle weakness
  • Snoring
  • Sweating and body odor
  • Thickening of the skin, skin tags
  • Trapped nerves (Carpal tunnel syndrome)

How long do I have to be monitored?

As long as you are considered to have abnormal (low or high) GH production or are receiving GH replacement therapy, your IGF-1 will need to be monitored.

Last Review Date: February 17, 2011