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Insulin-Like Growth Factor

Does this test have other names?

IGF, IGF-1

What is this test?

This test measures the amount of insulin-like growth factor-1 (IGF-1) in your blood.

IGF-1 is a hormone found naturally in your blood. Its main job is to regulate the effects of growth hormone (GH) in your body. Normal IGF-1 and GH functions include tissue and bone growth.

IGF-1 is formed in different tissues as a result of GH in the blood. Some disorders and diseases, such as pituitary tumors, can cause your body to make too much GH. Because IGF-1 measurements relate to GH measurements, this test is used to diagnose many problems linked to too much or too little GH.

Why do I need this test?

You may need this test if your healthcare provider suspects that you have or are at risk for a GH-related disease, including:

  • Acromegaly, or GH over-production, which causes too much growth of the hands, feet, and facial bones in adults

  • Laron syndrome, a condition in which GH doesn't work the way should, resulting in short stature

What other tests might I have along with this test?

Your healthcare provider may also order these tests:

  • X-rays to measure your bone age

  • Thyroid function tests to rule out thyroid problems

  • Other tests to check GH levels (insulin-like growth factor binding protein-3, IGFBP-3) 

Children may have clonidine, arginine, or glucagon blood tests.

What do my test results mean?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

IGF-1 measurements are adjusted for age because levels tend to decrease as you get older.

Results of IGF-1 are given in nanograms per milliliter (ng/mL). Normal ranges vary by age.

For diagnosing acromegaly:

  • If your IGF-1 is normal, but your GH is low, you likely don't have acromegaly.

  • If your IGF-1 is high and your GH is high, you may have acromegaly.

Levels of IGF-1 that are higher or lower than normal may also be caused by:

  • Hypothyroidism, or low thyroid hormone levels

  • Liver disease

  • Uncontrolled diabetes mellitus

How is this test done?

The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore. 

What might affect my test results?

Malnutrition or fasting (not eating) will affect your results. Age also affects your results; both IGF-1 and GH decline with age.

How do I get ready for this test?

You don't need to prepare for this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. 

Medical Reviewers:

  • Haldeman-Englert, Chad, MD
  • Taylor, Wanda, RN, Ph.D.