Patient Test Information

IGF-1

Also known as:

Somatomedin C

Formal name:

Insulin-like Growth Factor - 1

Related tests:

Growth Hormone, Growth Hormone Releasing Hormone, Glucose Tests, Glucose Tolerance Test, Free T4, TSH, IGFBP-3

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Why Get Tested?

To help diagnose growth hormone (GH) deficiency or, less commonly, growth hormone excess; to evaluate pituitary function; to monitor the effectiveness of GH treatment

When to Get Tested?

When a child has signs and symptoms of slow growth, short stature, and delayed development or an adult has decreased bone density, reduced muscle strength, and increased lipids that suggest insufficient GH and IGF-1 production; when a child or adult has signs and symptoms of gigantism or acromegaly, respectively, that suggest excess GH and IGF-1 production; during and after treatment for GH abnormalities; when a pituitary disorder is suspected

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

Generally none, unless instructed to fast

How is it used?

A test for insulin-like growth factor-1 (IGF-1) may be used to help:

  • Identify growth hormone (GH) deficiency; it is not diagnostic of a GH deficiency but may be ordered along with GH stimulation tests to offer additional information.
  • As follow-up to abnormal results on other hormone tests
  • Evaluate pituitary function

Less commonly, IGF-1 tests may be used to detect excess growth hormone and to help diagnose and monitor treatment of two rare conditions, acromegaly and gigantism.

IGF-1 is a hormone that, along with growth hormone, helps promote normal bone and tissue growth and development. An IGF-1 test is often ordered along with GH. IGF-1 mirrors GH excesses and deficiencies, but the level in the blood is stable throughout the day, making it a useful indicator of average GH levels.

IGF-1 may be ordered with other pituitary hormone tests, such as prolactin or FSH and LH, to help diagnose pituitary gland dysfunction and decreased pituitary hormones (hypopituitarism).

IGF-1 testing and a GH suppression test can be used to detect and monitor treatment of a GH-producing pituitary tumor. An anterior pituitary tumor is typically confirmed with imaging scans that help identify and locate the tumor. If surgery is necessary, GH and IGF-1 levels are measured after the tumor's removal to determine whether the entire tumor 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 a normal or near normal concentration. IGF-1 may be ordered to monitor the effectiveness of this therapy at regular intervals for years afterward to monitor GH production and to detect tumor recurrence.

IGF-1 levels and the measurement of GH can also provide information related to GH insensitivity. Prior to performing definitive GH testing, if the IGF-1 level is found to be normal for age and sex, GH deficiency is excluded and definitive testing is not necessary.

When is it ordered?

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
  • Adults have symptoms that a health practitioner suspects may be due to a GH deficiency, such as decreased bone density, fatigue, adverse changes to lipid levels, and reduced exercise tolerance. However, testing for IGF-1 deficiency is not routine in adults who have these symptoms; GH and IGF-1 deficiency are only very rare causes of these disorders.

An IGF-1 also may be ordered when a health practitioner suspects that someone has an underactive pituitary gland and at intervals to monitor those on GH therapy.

Less commonly, IGF-1 testing may be ordered, along with a GH suppression test, when a child has symptoms of gigantism or when an adult shows signs of acromegaly.

When a GH-producing pituitary tumor is found, GH and IGF-1 are ordered after the tumor is surgically removed to determine whether all of the tumor has been extracted. IGF-1 also is ordered at regular intervals when someone 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 person's GH production and to watch for pituitary tumor recurrence.

What does the test result mean?

A normal level of IGF-1 must be considered in context. Some people can have a GH deficiency and still have a normal IGF-1 level.

Decreased IGF-1
If the IGF-1 level is decreased, then it is likely that there is a 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 levels may reflect a GH deficiency or insensitivity.

If a decrease in IGF-1 is suspected to be due to a more general decrease in pituitary function (hypopituitarism), then several other endocrine glands and their pituitary regulating hormones will need to be evaluated to decide on appropriate treatment. Reduced pituitary function may be due to inherited defects or can develop 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 estrogen.

Increased IGF-1
Elevated levels of IGF-1 usually indicate an increased production of GH. Since GH levels vary throughout the day, IGF-1 levels are a reflection of average GH production, not of the actual amount of GH in the blood at the time that the sample for the IGF-1 measurement was taken. This is accurate up to the point at which the liver's capacity to produce IGF-1 is reached. With severely increased GH production, the IGF-1 level will stabilize at an elevated maximum level.

Increased levels of GH and IGF-1 are normal during puberty and pregnancy but otherwise are most frequently due to pituitary tumors (usually benign). 

If IGF-1 is still elevated after the surgical removal of a pituitary tumor, then the surgery may not have been fully effective. Decreasing IGF-1 levels during subsequent drug and/or radiation therapies indicate that the treatment is lowering GH production. If levels of IGF-1 become "normalized," then the person is no longer producing excess amounts of GH. When someone is undergoing long-term monitoring, an increase in IGF-1 levels may indicate a recurrence of the pituitary tumor.

Is there anything else I should know?

If an IGF-1 level is normal and a health practitioner still strongly suspects a GH deficiency, then the healthcare provider may order another test, an IGFBP-3 (insulin-like growth factor binding protein 3), to help confirm the GH deficiency. Almost all IGF-1 in the blood is bound to binding proteins, with IGFBP-3 being the most prevalent form, and IGFBP-3 production is also stimulated by GH.

What is being tested?

Insulin-like growth factor-1 (IGF-1) is a hormone that, along with growth hormone (GH), helps promote normal bone and tissue growth and development. The test measures the amount of IGF-1 in the blood.

IGF-1 is produced by the liver and skeletal muscle as well as many other tissues in response to GH stimulation. IGF-1 mediates many of the actions of GH, stimulating the growth of bones and other tissues and promoting the production of lean muscle mass. Since GH is released into the blood in pulses throughout the day, it is difficult to interpret the results from a single GH test. IGF-1 mirrors GH excesses and deficiencies, but unlike GH, its level is stable throughout the day. This makes IGF-1 a useful indicator of average GH levels. The IGF-1 test is therefore often used to help evaluate for GH deficiency or GH excess.

IGF-1 levels, like GH, 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 a dysfunctional pituitary gland with decreased pituitary hormones (hypopituitarism) or by the presence of a non-GH-producing pituitary tumor 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, hypothyroidism, sex hormone deficiency, and chronic diseases. Genetic GH insensitivity (GH resistance) is very rare.

IGF-1 deficiencies early in life, usually the result of GH deficiency, 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 density, less muscle mass, and altered lipid levels. However, testing for IGF-1 deficiency, or GH deficiency, is not routine in adults who have decreased bone density and/or muscle strength or increased lipids. GH deficiency and consequent IGF-1 deficiency is a very rare cause of these disorders.

Excess GH and IGF-1 can cause abnormal growth of the skeleton and other signs and symptoms characteristic of two rare conditions, 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 risk of cardiovascular disease, high blood pressure, arthritis, and a decreased lifespan.

The most common reason for the pituitary to secrete excessive amounts of GH is a GH-producing pituitary tumor (usually benign). Frequently, the tumor 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 the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

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.

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

    In a child, it is unusual tallness. 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)
  3. Can this test be done in my doctor's office?

    No, this test requires specialized equipment and training and is not available in every laboratory. Your blood may be sent to a reference laboratory.

  4. 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. However, IGF-1 is not routinely measured to monitor GH treatment of GH-deficient children. The best index of the effectiveness of GH treatment of children who are GH-deficient is observation of an increase in their growth rate and their absolute height.