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Insulin-Like Growth Factor

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Insulin-Like Growth Factor

Does this test have other names?

IGF

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 have this test if your doctor 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 doctor 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

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

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

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 by age are:

  • 182 to 780 ng/mL for ages 16 to 24

  • 114 to 492 ng/mL for ages 25 to 39

  • 90 to 360 ng/mL for ages 40 to 54

  • 71 to 290 ng/mL for people 55 and older

For diagnosing acromegaly:

  • If your IGF-1 is normal, but your GH is less than 0.3 g/L, you likely don't have acromegaly.

  • If your IGF-1 is higher and your GH is above 0.3 g/L, you likely 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 requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly 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.