Also Known As
Somatomedin C
Formal Name
Insulin-like Growth Factor-1
This article was last reviewed on
This article waslast modified on 3 July 2023.
At a Glance
Why Get Tested?

To identify diseases and conditions caused by deficiencies and overproduction of growth hormone (GH), to detect disease of the pituitary gland, and to monitor the effectiveness of growth hormone replacement treatment

When To Get Tested?

As part of an evaluation of pituitary function;
1. When you are growing more slowly than normal, have short stature, have delayed development (in children) or decreased bone density, reduced muscle strength, and increased lipids (in adults), all of which suggest insufficient GH and IGF-1 production
2. When you have symptoms of gigantism (in children) or acromegaly (in adults) that suggest excess GH and IGF-1 production
3. During and after treatment for GH abnormalities

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?

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.

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

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 which are small proteins made up of a small chain of amino acids. IGF-1 and GH are vital for normal bone and tissue growth and development. GH is produced by the pituitary gland, a grape-sized gland which sits at 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 in response to GH stimulation and mainly comes from the liver with a little from muscles. It mediates many of the actions of GH, stimulating the growth of bones and other tissues and increasing the production of muscle mass. IGF-1 excesses and deficiencies mirrors those of GH, but its level does not fluctuate during the day as does GH which makes 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 as a consequence of 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 collected by inserting a needle into a vein in your arm.

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.

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Common Questions
  • 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 used 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 used 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. Presence of a tumour is confirmed with imaging scans that help identify and locate the tumour. If surgery is necessary, GH and IGF-1 levels are measured after removal of the tumour to find out 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 used, 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 requested when adults have symptoms that the doctor suspects may be due to a GH deficiency. An IGF-1 also may be used 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 requested 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 used after the tumour is surgically removed to find out whether all of the tumour has been removed. IGF-1 is also used at regular intervals when a patient is having drug and/or radiation therapy that is frequently used follow tumour surgery.

    IGF-1 levels may be requested at regular intervals for many years to monitor a patient’s GH production and to watch for recurrence of a pituitary tumour.

  • What does the test result mean?

    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 other 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 at the time of sampling. 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 return to normal then the patient no longer produces excess amounts of GH. When a patient has 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 GH deficiency, then they may request another test, such as an IGFBP-2 or IGFBP-3 (insulin-like growth factor binding protein 2 or 3), to help confirm the GH deficiency. 

  • 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 age
    • Delayed puberty
    • X-rays showing delayed bone development
    In adults, abnormally low levels of GH and/or IGF-1 may cause subtle, non-specific symptoms such as:
    • Decreased bone density
    • Tiredness
    • Marked changes in lipid levels
    • 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 odour
    • 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.

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