Insulin-Like Growth Factor
Does this test have other names?
IGF, IGF-1, somatomedin C
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 manage the effects of growth hormone (GH) in your body. IGF-1 and GH are important for tissue and bone growth.
IGF-1 is produced by different tissues under the control of GH. Some disorders and diseases, such as pituitary tumours, can cause your body to make too much or too little GH. IGF-1 measurements relate to GH measurements. Because IGF-1 does not fluctuate as much as GH and is more stable, IGF-1 is the preferred test used to screen for 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 disorder, including:
- Acromegaly. This condition is caused by too much GH being produced in adulthood. This causes too much growth of the hands, feet, and facial bones.
- Gigantism. This condition is caused by too much GH being produced during childhood. Children with gigantism grow very tall for their age.
- GH deficiency. This condition is caused by too little GH being produced. In children, this causes slow growth, and children are shorter for their age. In adults, this can lead to low bone density and reduced muscle mass.
- GH resistance (Laron syndrome). This is a rare condition where the body is not sensitive to GH due to a variant (difference) in the growth hormone receptor gene. The variant prevents GH from carrying out its biological actions. This results in decreased IGF-1 and short stature (dwarfism).
This test also helps to monitor how well the GH treatment is working.
What other tests might I have along with this test?
You may also need these tests:
- X-rays to measure your bone age
- Pituitary hormone tests to rule out pituitary, thyroid, and other hormone conditions
- Tests involving GH stimulation or suppression to diagnose GH deficiency or excess (these are called confirmatory tests)
- Other tests to check GH levels, including random GH or insulin-like growth factor binding protein-3 (IGFBP-3)
What do my test results mean?
Each laboratory has different ranges for what’s normal. The ranges are also different based on age and sex. Your lab report should show the ranges that your laboratory uses for each test. Because IGF-1 changes with age and sex, it is important to interpret results based on the normal ranges provided by the laboratory for each of these factors.
The normal range is just a guide. Your doctor will also look at your results based on your age, sex, health, and other factors. A value that isn't in the normal range may still be normal for you.
- If your results show low IGF-1 level, it may indicate GH deficiency or resistance.
- If your results show high IGF-1 level, it may indicate an overproduction of GH or excessive GH replacement therapy.
Your healthcare provider may order more tests to help make a diagnosis.
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.
Does this test pose any risks?
Having a blood test with a needle is generally safe. Some people may have bruising, bleeding, or feeling light-headed. When the needle pricks your arm, you may feel a slight sting or pain. Afterward, the site may be sore.
What might affect my test results?
Malnutrition or not eating (fasting) will affect your results. Age also affects your results, as both IGF-1 and GH decline after puberty.
How do I get ready for this test?
You don't need to get ready for this test. Be sure your health care provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.
Adaptation Date: 06/29/2026
Adapted By: Alberta Health Services
Adaptation Reviewed By: Alberta Health Services
