A somatomedin C test, also called an insulin-like growth factor-1 (or IGF-1) test,
helps doctors evaluate whether a person is producing a normal amount of human growth
hormone (hGH, or somatotropin).
HGH is produced by the pituitary gland, the pea-sized gland in the brain that helps
control growth and the function of other glands. Somatomedin C is a protein produced
in the liver and muscles that's known as a growth factor — its production is
stimulated by hGH.
While hGH levels vary throughout the day depending on diet and activity levels,
somatomedin C levels in the blood are more stable, making its measurement a fairly
reliable indicator of how much hGH the pituitary gland is producing overall.
Why It's Done
The somatomedin C test is primarily ordered to check for pituitary gland disorders
and abnormalities in growth hormone production. Symptoms such as short stature or
excessive growth (gigantism) may warrant a somatomedin C test.
The test may also be used to assess a child's nutritional status, because malnutrition
may reduce somatomedin C levels.
Your child may be asked to stop eating and drinking for 10 to 12 hours before this
test. On the day of the test, having your child wear a T-shirt or short-sleeved shirt
can make things easier for your child and the technician who will be drawing the blood.
A health professional will clean the skin surface with antiseptic, and place an
elastic band (tourniquet) around the upper arm to apply pressure and cause the vein
to swell with blood. A needle is inserted into a vein (usually in the arm inside of
the elbow or on the back of the hand) and blood is withdrawn and collected in a vial
After the procedure, the elastic band is removed. Once the blood has been collected,
the needle is removed and the area is covered with cotton or a bandage to stop the
bleeding. Collecting blood for this test will only take a few minutes.
What to Expect
Collecting a sample of blood is only temporarily uncomfortable and can feel like
a quick pinprick. Afterward, there may be some mild bruising, which should go away
in a few days.
Getting the Results
The blood sample will be processed in a laboratory. Because this isn't a common
test, the results may not be available from the lab until a week or two after the
sample is drawn.
The somatomedin C test is considered a safe procedure. However, as with many medical
tests, some problems can occur with having blood drawn, such as:
fainting or feeling lightheaded
hematoma (blood accumulating under the skin causing a lump or bruise)
pain associated with multiple punctures to locate a vein
Helping Your Child
Having a blood test is relatively painless. Still, many children are afraid of
needles. Explaining the test in terms your child can understand might help ease some
of the fear.
Allow your child to ask the technician any questions he or she might have. Tell
your child to try to relax and stay still during the procedure, as tensing muscles
and moving can make it harder and more painful to draw blood. It also may help if
your child looks away when the needle is being inserted into the skin.
If You Have Questions
If you have questions about the somatomedin C test, speak with your doctor.