GH testing is not recommended for general screening. It is primarily ordered on those with symptoms of growth hormone abnormalities, as a follow-up to other abnormal hormone test results, or to help evaluate pituitary function.

Periodic GH measurements may also be performed on children who have had radiation treatment of the central nervous system or whole body irradiation prior to stem cell transplants. This is common in acute lymphoblastic leukemia (ALL), where irradiation of the brain can affect the hypothalamus and pituitary gland, thus affecting growth.

Growth hormone tests help identify excess and diminished GH production and give your doctor information about the severity of your condition. They are part of the diagnostic work-up required to find a cause for abnormal hormone production. Testing most often involves either a GH stimulation test or a GH suppression test to track GH levels over time.

GH stimulation tests help to diagnose hypopituitarism. For a stimulation test, a sample of blood is drawn after you have fasted for 10-12 hours. Then, under close medical supervision, you are given an intravenous solution of insulin or arginine. Blood samples are then drawn at timed intervals, and GH levels are tested in each to see if your pituitary gland was stimulated by the insulin (or arginine) to produce expected levels of GH.

GH suppression tests help to diagnose hyperpituitarism, which, in addition to other blood tests and imaging scans, can help identify and locate pituitary tumors. For a suppression test, a sample of blood is drawn after you have fasted for 10-12 hours. Then you are given a standard glucose solution to drink. Blood samples are drawn at timed intervals, and GH levels are tested in each to see if your pituitary gland is sufficiently suppressed by the dose of glucose.

Often other blood tests that reflect pituitary function, such as T4, TSH, cortisol, FSH, LH, and testosterone (in men), are also ordered. These tests are usually performed prior to GH testing to make sure that they are normal and/or controlled with medication before GH testing is done. Glucose levels are run on the samples collected during the GH suppression test, both to track glucose levels and to make sure that the patient’s system is sufficiently challenged by the glucose solution.

IGF-1 (Insulin-like growth factor – 1) is often measured once during GH provocation testing and is often used by itself or with GH as a monitoring tool. Produced in the liver, IGF-1 mirrors GH excesses and deficiencies, but its level is stable throughout the day, making it a useful indicator of average GH levels.

GH and IGF-1 levels are often monitored for extended periods of time following treatment for GHD, gigantism, and acromegaly, and are monitored following surgery, drug treatment, and/or radiation for a pituitary tumor.

GH stimulation testing is ordered when your child has symptoms of GHD, such as when:

• his growth rate slows down in early childhood and he is significantly shorter than others his age;
• TSH tests show that your child is not hypothyroid (low thyroid levels can also cause slowed growth);
• X-rays show delayed bone development;
• your doctor suspects that your child’s pituitary gland is under-active.

Once GHD is diagnosed, your doctor may use stimulation testing to confirm the diagnosis, along with IGF-1 to monitor the effectiveness of GH replacement (if indicated), and as a child reaches adulthood to see if continued supplementation is necessary.

GH levels are also monitored in children who have received radiation therapy.

Stimulation testing is ordered in adults when patients have symptoms of GHD and/or hypopituitarism, such as decreased bone density, fatigue, adverse lipid changes, and reduced exercise tolerance. Other hormone testing is done first to rule out other conditions that may cause similar symptoms.

GH suppression testing is done when children show signs of gigantism, when adults show signs of acromegaly, and/or when their doctor suspects hyperpituitarism. Suppression testing may be done when a pituitary tumor is suspected and may be used along with IGF-1 levels and other hormone levels to monitor the effectiveness of treatment for these conditions. Monitoring may continue at regular intervals for many years to watch for recurrence.

Since GH is released by the pituitary in bursts, random GH levels are not very useful. There is too much overlap between abnormal results and normal daily variation. GH levels will be higher first thing in the morning and will increase with exercise and stress.

GH suppression test:
If your GH levels are not significantly suppressed during a GH suppression test (they stay higher than they should) and:

• you have symptoms of gigantism or acromegaly
• other pituitary hormone levels are normal and/or controlled
• your IGF-1 levels are high

then it is likely that you are producing too much GH and it is causing complications. If you have other pituitary hormones that are abnormal, then you may have a condition causing hyperpituitarism. If a mass shows up on an X-ray, CT scan, or MRI, then you may have a pituitary tumor (or very rarely a malignancy). If you are being monitored for a previous tumor, then you may be having a recurrence.

GH stimulation test:
If your GH levels are not significantly stimulated during a GH stimulation test (they stay lower than they should) and:

• you have symptoms of GHD
• other pituitary hormone levels are normal and/or controlled
• your IGF-1 level is low

then it is likely that you have a deficiency of GH that your doctor may treat. If your TSH level is low, then that should be addressed first as thyroid deficiencies can cause symptoms similar to GHD. You may also have a more general decrease in pituitary function.

Pituitary tumors are the most common cause of excess GH production but may also cause deficiencies. Presence of a pituitary tumor not only can affect GH production, but may also affect production of other pituitary hormones, such as ACTH (Cushing’s syndrome) or prolactin (galactorrhea). If the tumor is relatively large, it may inhibit all pituitary hormone production and cause damage to the surrounding tissues.

Factors that can interfere with GH testing include:

• Stress, exercise, and low blood glucose levels
• Drugs that can increase GH include: amphetamines, arginine, dopamine, estrogens, glucagon, histamine, insulin, levodopa, methyldopa, and nicotinic acid
• Drugs that can decrease GH levels: corticosteroids and phenothiazines
• Radioactive scan within week of test (with some laboratory methods)

Abnormal GH levels can usually be modified once the causes are identified. Synthetic GH is available to alleviate deficiencies in children (treatment of adults with GHD is more controversial). Combinations of surgery, medication, and radiation can be used to treat pituitary tumors that are causing excess GH production. The important thing is to identify GH abnormalities as soon as possible for good outcomes. The bone growth changes associated with gigantism and acromegaly are permanent and, if left untreated, the GH deficient child’s short stature will remain.

There can be long term complications from GH abnormalities. Acromegaly, for instance, can cause colon polyps (increasing a patient’s risk of developing colon cancer), diabetes, high blood pressure, and visual abnormalities. If a pituitary tumor permanently damages pituitary cells, then multiple hormone replacement may be necessary. Increased bone growth may also lead to trapped nerves (carpal tunnel syndrome), arthritis, and weak bones.