IGF-1 (Insulin-like Growth Factor 1) Test
Reviewed
Also called: Somatomedin C test, IGF-1 test
This test measures the amount of insulin-like growth factor 1 (IGF-1) in your blood. IGF-1 helps manage the effects of growth hormone and promotes normal growth of bones and tissues. The test is used to detect and monitor growth hormone disorders such as deficiency, insensitivity, gigantism, and acromegaly. Because IGF-1 levels are more stable than growth hormone levels, this test provides a reliable way to assess growth hormone status.
Specimen: Blood
Why this test may be ordered
- To evaluate symptoms of growth hormone disorders in children (e.g., slowed growth, short stature) or adults (e.g., fatigue, low bone density, enlarged hands/feet, coarse facial features).
- To monitor treatment for known growth hormone disorders.
Preparation and collection
You don't need any special preparations for 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.
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.
Understanding results
Your healthcare provider will interpret your IGF-1 test results based on your age, sex, and other factors. The following patterns are common but are not diagnoses.
- Lower than normal IGF-1 level: Lower than normal IGF-1 level Limitation: This pattern may be due to growth hormone deficiency or insensitivity in children, or normal age-related decline in adults. It does not diagnose a condition alone. Next step: Your provider may order a growth hormone stimulation test or IGFBP-3 test to clarify the cause.
- Higher than normal IGF-1 level: Higher than normal IGF-1 level Limitation: This pattern may indicate gigantism (children) or acromegaly (adults), often from a pituitary tumor. It is not a confirmed diagnosis. Next step: Your provider may order a growth hormone suppression test, IGFBP-3 test, and pituitary imaging to confirm the cause.
- IGF-1 levels change normally with age (low in childhood, peak during puberty, decrease in adulthood).
- Lower than normal levels may be due to growth hormone deficiency, growth hormone insensitivity, or normal age-related decline.
- Higher than normal levels may indicate gigantism (children) or acromegaly (adults), often from a pituitary tumor.
- Interpretation requires correlation with clinical findings and additional tests (e.g., GH stimulation/suppression test, IGFBP-3 test).
What to do next
Your healthcare provider will interpret the results in the context of your symptoms, age, and other tests. Further evaluation may include GH stimulation or suppression tests, IGFBP-3 test, or imaging to check for pituitary tumors.
- What are the symptoms that led to ordering this test?
- What is my age and how does it affect the interpretation?
- Will I need additional tests to confirm the diagnosis?
- What treatment options are available if the results are abnormal?
Evidence source
U.S. National Library of Medicine: IGF-1 (Insulin-like Growth Factor 1) Test