What is being tested?
Growth hormone (GH) is essential for a child’s normal growth and development and promotes proper linear bone growth from birth through puberty. Children with insufficient GH production grow more slowly and are smaller in size for their age, one of the first symptoms of growth hormone deficiency (GHD). It should be noted that short stature in itself can also be related to familial traits or other genetic disorders. Excess GH is most often due to a GH-secreting pituitary tumor (usually benign). Too much GH can cause children’s long bones to continue to grow beyond puberty, resulting in gigantism with heights of 7 or more feet tall. Those with excess GH may also have thickening of facial features, general weakness, delayed puberty, and headaches.

Although GH is not as active in adults, it does play a role in regulating bone density, muscle mass, and lipid metabolism. Deficiencies can lead to decreased bone densities, less muscle mass, and altered lipid levels. Excess GH in adults can lead to acromegaly, marked not by bone lengthening but by bone thickening. Although symptoms such as skin thickening, sweating, fatigue, headaches, and joint pain can be subtle at first, increased GH levels can lead to enlarged hands and feet, enlarged facial bones, carpal tunnel syndrome, and abnormally enlarged internal organs. If untreated, acromegaly (and gigantism in children) can lead to complications such as type 2 diabetes, increased cardiovascular disease risk, high blood pressure, arthritis, and in general, a decreased life span.

GH stimulation and suppression tests are most often used to diagnose GH abnormalities. Since growth hormone is released by the pituitary gland in bursts throughout the day, random measurements of GH levels are not usually clinically useful.

How is the sample collected for testing?
Usually GH suppression or stimulation testing is done. After you have fasted for 10 to 12 hours, a blood sample is drawn from a vein in your arm. Then, under medical supervision, you are given either a standard glucose solution to drink (for a suppression test) or you are given an intravenous (IV) solution of insulin or arginine (for a stimulation test) through a vein in your arm. Blood samples are then drawn from your veins (or from the IV) at timed intervals. GH tests are run on each sample collected to monitor the change in levels of growth hormone over time.

Sometimes, a single sample of blood is drawn following a fast or after a period of strenuous exercise.

Is any test preparation needed to ensure the quality of the sample?
In healthy adults, GH levels remain stable, but rise sharply 3-4 hours after a meal and within 60 minutes after sleep. Thus, one should be fasting before testing.