Somatomedin C (IGF-1) Blood Test

Also called: Insulin-Like Growth Factor-1 Test, IGF-1 Test, Somatomedin C Test

Somatomedin C (IGF-1) Blood Test

What Is a Somatomedin C Test & Why Is It Done?

A somatomedin (so-muh-toe-MEE-den) C test measures the level of a protein in the blood called somatomedin C. The test helps show if the body is making a normal amount of growth hormone (GH). This is a substance the pituitary gland makes that helps kids grow and develop.

Doctors usually order the test to:

• look for pituitary gland disorders and problems with growth hormone production (like short stature or excessive growth, also called gigantism)
• monitor how GH treatment is working

Doctors may recommend the test for kids who are much smaller or larger for their age than expected.

What Is Somatomedin C?

Somatomedin C (also called insulin-like growth factor-1, or IGF-1) is a protein made mostly in the liver. It helps cells grow and divide in response to stimulation by GH, also called somatotropin (STH). 

While GH levels vary throughout the day depending on a person’s diet and activity levels, somatomedin C levels in the blood are more stable. So measuring it is a way for doctors to see how much GH the pituitary gland is making. The GH level is highest at puberty.

Top Things to Know

• The somatomedin C blood test shows how much somatomedin C (a protein) is in the blood.
• The tests helps look for problems with the pituitary gland, growth hormone, and nutrition, and to check on growth disorder treatment.
• Kids might need to stop taking certain medicines or not eat or drink before the blood test.
• Your doctor can explain what it means if somatomedin C levels are low or high.

How Can I Help My Child Prepare for a Blood Test?

To help kids get ready for a blood test, find out if they need to fast (not eat or drink) or should stop taking medicines before the test. Explain what to expect during the test. If your child is nervous about it, work together on ways to stay calm. Deep breathing or even imagining being in a place that makes your child feel safe and relaxed can help.

What Do Somatomedin C Test Results Mean?

Your doctor will explain what the results of the test mean for your child. What’s “normal” can vary based on things like age and gender.

Low Somatomedin C Level

A low level of somatomedin C could be due to things like:

• growth hormone deficiency (when the pituitary gland makes too little GH)
• Laron syndrome, or growth hormone insensitivity (a genetic condition where the body doesn’t respond to growth hormone as it should)
• poor nutrition

High Somatomedin C Level

A high level of somatomedin C could be due to things like a pituitary gland problem, which can cause gigantism.

What Else Should I Know?

When kids have a somatomedin C test, they may also need other tests, like a IGF binding protein-3 (IGFBP-3) blood test.

If you have questions about the somatomedin C test or what the results mean, talk to your doctor.