Insulin-like growth factor 1 (IGF-1)

A growth hormone (GH) test measures the amount of human growth hormone (GH) in the blood. GH is made by the pituitary gland and is needed for growth. It plays an important role in how the body uses food for energy (metabolism). Growth hormone can cause the release of other substances (factors) that affect growth and metabolism. One of these is insulin-like growth factor 1 (IGF-1). When the GH level is very high, the IGF-1 level is also very high. A test for IGF-1 may also be done to confirm high GH levels.

Why it is done?

A test for growth hormone (GH) is done to:

  • See whether a child whose growth is abnormal has dwarfism or gigantism.
  • See whether an adult has acromegaly. This condition is caused by a tumor (adenoma) of the pituitary gland.
  • Check treatment that uses growth hormone.

How to prepare:

There’s no special preparation required before the test but make sure you tell the doctors about all the nonprescription and prescription medicine you take.

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How it is done

Insulin-like growth factor 1 Increase levels of IGF-1, and it may be the first test done.

The health professional drawing blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

The Risk:

There is very little chance of a problem from having a blood sample taken from a vein.

  • You may get a small bruise at the site.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis.
  • Ongoing bleeding can be a problem for people with bleeding disorders.

What affects the test?

  • Taking medicines, such as amphetamines, corticosteroids, insulin, or estrogens.
  • Having low blood sugar (hypoglycemia).
  • Being obese.
  • Taking the herb St. John’s wort.

What to think about:

Normal levels of growth hormone (GH) change during the day so other tests may be done to confirm the results of a GH test.

  • A high level of IGF-1 with a high level of GH generally means acromegaly is present.
  • The growth hormone suppression test (also called the glucose loading test) measures the level of GH in the blood before and after a person drinks fluid with a large amount of sugar (glucose) in it.

The growth hormone stimulation test measures the level of GH in the blood before and after insulin or arginine is given in a vein (intravenously) in the arm.