Understanding GH and IGF-1 Levels

By Acromegaly Answers Blog Staff

Recently, the writers at Acromegaly Answers (a Web log owned and operated by Ipsen) spoke with Daphne Adelman, a nurse at Northwestern University in Chicago, about growth hormone (GH) and insulin-like growth factor-1 (IGF-1) levels, what they are, how you test them, and what happens when there’s too much in your body.

Let’s define our terms: growth hormone and insulin-like growth factor-1

• Growth hormone is a hormone made in the pituitary gland. In addition to signaling the body that it is time to grow, GH stimulates the production of another hormone, insulin-like growth factor-1. This hormone is produced by the liver and other tissues. Both hormones produce growth in the body’s bones, organs, and tissues.
• Insulin-like growth factor-1, as its name implies, is a hormone similar in structure to insulin. IGF-1 plays an important role in childhood growth and continues to have effects in adults. Higher-than-normal amounts of IGF-1 are caused by too much GH in the body, which stimulates the liver and other tissues to produce extra IGF-1.

Testing your levels of GH
Testing your levels of GH to see if there’s too much is typically done with an oral glucose tolerance test (OGTT). An OGTT works like this: you fast for 8-14 hours before the test, usually overnight. When you come in for the test, you give a blood sample. This sample is used to find your “baseline” blood level of GH. Then you drink a glucose (the main body sugar) solution over 5 minutes. You give more blood samples for GH measurements at 30 minutes, 60 minutes, 90 minutes, and 120 minutes after drinking the glucose.

Most patients’ bodies respond to the glucose by suppressing or holding down the GH in their blood to levels so low, they can’t be measured. If you have acromegaly, your GH levels are not suppressed, and may even rise, during a glucose tolerance test.

Normal GH and IGF-1 levels for an adult
According to Daphne Adelman, a nurse at Northwestern University in Chicago, GH levels in adults shouldn’t go above 1 nanogram per milliliter (>1ng/mL) of blood, and IGF-1 should stay below about 300 nanograms per milliliter. She also made the point that the normal range varies from assay to assay. (An assay is a blood test done to determine the presence and amount of GH in your bloodstream. Different assays use different methods to test and have different normal ranges.)

Now, 300 nanograms-per-milliliter doesn’t sound like much, but GH and IGF-1 are powerful chemicals at work in your body. Age also plays a role in testing. IGF-1 levels vary with age, declining as you get older. What might be a normal level of IGF-I in your 20’s could be considered too high in your 40’s or 50’s.

When there is too much IGF-1, acromegaly occurs
Too much IGF-1 is usually caused by too much growth hormone, which is generally the result of a tumor on your pituitary gland. The surplus GH stimulates your liver and other tissues to produce more IGF-1 than your body needs. Together, too much GH and too much IGF-1 cause your organs and bones to grow, even after they should have stopped, and when that happens, the diagnosis is acromegaly.

There are treatment options if you have a diagnosis of acromegaly
Currently, surgery to remove the tumor on your pituitary gland is the first treatment recommended for patients with acromegaly.

Beyond surgery (or instead of surgery, if you’re not a good candidate for surgery), another option is treatment with medicine. Over the last 20 years, very selective medicines called somatostatin analogs, or SSAs, have been developed. SSAs lower GH and IGF-1 levels for a lot of patients with active acromegaly. An SSA is typically prescribed after surgery if the operation doesn’t bring down your GH and IGF-I levels. Your doctor might also prescribe an SSA as the first treatment for you if you prefer not to have surgery, if you’re too ill to have surgery, or if your tumor is inoperable.

Radiation aimed at the tumor is sometimes used to treat acromegaly. SSAs are also used after radiation therapy, which can take a long time to be effective. During that long period, an SSA might be prescribed to bring down your GH and IGF-1 levels.

A test every year for IGF-1 levels is a necessity
As a nurse who sees acromegaly patients, Daphne Adelman makes the point that acromegaly is a chronic condition and routine testing is necessary to make sure that your treatment is working. She advised meeting with your doctor once or twice a year. If your GH and IGF-1 levels are going up or fluctuating up and down, you should see your doctor more often. You need to make sure that your medication is adjusted properly.

After getting a diagnosis and finding the right treatment for acromegaly, you might feel better, and think about skipping your annual blood test, but don’t do it. There is always the chance that your medication stopped working, or a tumor started growing back. As Daphne reminds us, without regular testing, you might not know it; annual testing is the best way to catch things like that.

While we’re talking about skipping, if your medication’s working and you’re feeling better, you might also think about skipping doses of your medication. Once again, don’t do it. If you’re feeling better, it’s probably because your GH and IGF-1 levels are under control. Keeping them under control means taking your medication as directed by your doctor.

Now it’s your turn, Acromegaly Answers blog readers
If you have acromegaly, think you have acromegaly, or care for someone with acromegaly, consider these questions:

Note that articles on this blog are written by a contracted writer/editor. Daphne Adelman received compensation for her time helping to develop this blog post from Ipsen.