What is an IGF-1 test?

This test measures the amount of IGF-1 (insulin-like growth factor 1) in your blood. IGF-1 is a hormone that manages the effects of growth hormone (GH) in your body. Together, IGF-1 and GH promote normal growth of bones and tissues. GH levels in the blood fluctuate throughout the day depending on your diet and activity levels. But IGF-1 levels remain stable. So, an IGF-1 test is a useful way to find out if your body is making a normal amount of GH.

Other names: somatomedin C test

What is it used for?

An IGF-1 test is used to diagnose growth hormone disorders, including:

  • GH deficiency. In children, GH is essential for normal growth and development. A GH deficiency can cause a child to grow more slowly and be much shorter than children of the same age. In adults, GH deficiency can lead to low bone density and reduced muscle mass.
  • GH insensitivity, also known as Laron syndrome. This is a rare genetic disorder in which the body is unable to use the growth hormone it produces. It also causes slowed growth rate and shorter than normal height in children.
  • Gigantism. This is a rare childhood disorder that causes the body to produce too much growth hormone. Children with gigantism are very tall for their age and have large hands and feet.
  • Acromegaly. This disorder, which affects adults, causes the body to produce too much growth hormone. Adults with acromegaly have thicker than normal bones and enlarged hands, feet, and facial features.

Why do I need an IGF-1 test?

Your provider may order an IGF-1 test if you or your child has symptoms of a GH disorder.

Symptoms of GH deficiency or GH insensitivity in children include:

  • Slowed growth rate compared with children of the same age
  • Shorter height, arms, and legs, and lower weight than children of the same age
  • Small penis in males
  • Thin hair
  • Poor nail growth

Adults with GH deficiency may have symptoms such as fatigue and decreased bone density and muscle mass. But IGF-1 testing isn’t common for adults, as other disorders are much more likely to cause these symptoms.

Symptoms of GH excess (gigantism) in children include:

  • Excessive growth compared with children of the same age
  • Overly large head
  • Larger than normal hands and feet
  • Mild to moderate obesity

Symptoms of GH excess (acromegaly) in adults include:

  • Deep, husky voice
  • Larger than normal facial features such as lips, nose, and tongue
  • Excessive sweating and body odor
  • Thickening of bones
  • Coarse, oily skin
  • Irregular menstrual cycles in women
  • Erectile dysfunction in men

What happens during an IGF-1 test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for this test?

You don’t need any special preparations for an IGF-1 test.

Are there any risks to this test?

There is very little risk to you or your child in having a blood test. There may be slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If your child’s results show lower than normal levels of IGF-1, it probably means he or she has a GH deficiency or insensitivity to GH. In a child, this may be caused by a genetic disorder or brain disease. Your child may benefit from treatment with GH supplementation. GH supplementation is an injected medicine that contains manufactured human growth hormone. When GH deficiency is diagnosed and treated early, some children can grow several inches in the first year of treatment. Others grow less, and more slowly, but still benefit from treatment.

If your results show lower than normal IGF-1, it may be due to a normal age-related decrease in the hormone or other condition. Your provider may order more tests to help make a diagnosis.

Higher than normal levels of IGF-1 may mean gigantism in children or acromegaly in adults. Gigantism and acromegaly are most often caused by a tumor in the pituitary gland, a small organ in the base of the brain that controls many functions, including growth. Treatment for the tumor may include radiation therapy, surgery, and/or medicine. If the disorder was not caused by a tumor, you or your child may need more tests.