AMPATH Lab: What Is A Growth Hormone Suppression Test

What Is a Growth Hormone Suppression Test?

Your doctor may recommend a growth hormone suppression test if there is concern that your body is producing excessive levels of growth hormone (GH). While GH is essential for growth and development during childhood, abnormally high levels in adults or children can lead to serious medical conditions. This test is considered the most accurate method for confirming excess growth hormone production.

What Is a Growth Hormone Suppression Test?

A growth hormone suppression test is a diagnostic procedure used to determine whether the pituitary gland is producing too much growth hormone. It is commonly performed using an oral glucose tolerance method and is regarded as the gold standard test for diagnosing growth hormone excess.

Under normal circumstances, an increase in blood glucose levels signals the pituitary gland to suppress growth hormone release. During this test, blood sugar levels are intentionally raised to observe whether GH levels decrease appropriately. If growth hormone levels fail to suppress, it indicates abnormal hormone regulation, often due to a pituitary tumor.

This test is primarily used to diagnose the following conditions.

Acromegaly: A condition in adults caused by prolonged excess growth hormone, leading to enlargement of hands, feet, facial bones, and internal organs.

Gigantism: A rare condition in children and adolescents that occurs before growth plates close, resulting in excessive height and abnormal growth.

Why Might You Need This Test?

A growth hormone suppression test is typically ordered when blood tests show elevated growth hormone or insulin-like growth factor 1 (IGF-1) levels, or when symptoms suggest growth hormone excess. IGF-1 testing is often done first because its levels remain stable throughout the day, unlike GH, which is released in pulses.

Symptoms of Acromegaly in Adults

Acromegaly develops slowly, and symptoms may not be obvious initially. Common signs include enlargement of hands and feet, changes in facial features such as a prominent jaw or widened nose, increased spacing between teeth, thickened or oily skin, excessive sweating, joint pain, fatigue, muscle weakness, headaches, vision problems, and enlargement of internal organs including the heart.

Symptoms of Gigantism in Children

In children and adolescents, symptoms are mainly related to excessive growth. These may include rapid and abnormal height gain, enlarged hands and feet, coarse facial features, delayed puberty, headaches, and vision disturbances.

How to Prepare for the Test

Proper preparation is essential for accurate results. Your doctor will give you specific instructions before the test.

Fasting: You will usually be asked to fast for 8 to 12 hours before the test. Only water is allowed during this period.

Medications: Inform your doctor about all medications, supplements, or vitamins you are taking. Certain drugs, such as corticosteroids, estrogen-containing medications, and beta-blockers, can interfere with test results. Do not stop any medication unless advised by your healthcare provider.

Physical activity: Vigorous exercise can temporarily affect growth hormone levels. Avoid strenuous physical activity for at least 24 hours before the test.

What Happens During the Test?

The growth hormone suppression test is performed in a laboratory or clinic and usually takes about three hours.

A baseline blood sample is collected after inserting an intravenous line into your arm. This establishes fasting levels of growth hormone and glucose.

You will then be asked to drink a glucose solution containing a measured amount of sugar. The solution must be consumed within a short time frame.

Blood samples are drawn at regular intervals, typically every 30 minutes, over the next two to three hours to measure glucose and growth hormone levels.

During the test, you will be asked to rest quietly and avoid eating or physical movement. Small sips of water may be allowed.

Understanding the Test Results

The results are based on how your growth hormone levels respond to increased blood glucose.

Normal results: In healthy individuals, growth hormone levels suppress to very low values following glucose intake. Typically, GH levels drop below 1 ng/mL and often below 0.4 ng/mL during the test.

Abnormal results: If growth hormone levels do not suppress adequately, it suggests uncontrolled GH production. This finding strongly indicates acromegaly or gigantism, most commonly due to a pituitary adenoma.

If results are abnormal, your doctor may recommend imaging studies such as an MRI scan to identify the source of excess hormone production.

Conclusion

A growth hormone suppression test is a critical diagnostic tool for identifying growth hormone excess. Although the test requires several hours, it provides clear and reliable results that guide further evaluation and treatment.

If your doctor has advised this test or if you are experiencing symptoms suggestive of acromegaly or gigantism, early testing is essential. Prompt diagnosis allows timely treatment, helping prevent long-term complications and improve overall health outcomes.