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Introduction ⬇

Human growth hormone (somatotropin, hGH) is essential to the growth process and has an important role in the metabolism of adults. It is secreted by the pituitary gland in response to exercise, deep sleep, hypoglycemia, glucagon, insulin, and vasopressin. GH also stimulates the production of RNA, mobilizes fatty acids from fat deposits, and is intimately connected with insulinism. If the pituitary gland secretes too little or too much GH in the growth phase of life, dwarfism or gigantism will result, respectively. An excess of GH during adulthood leads to acromegaly.

This test confirms hypopituitarism or hyperpituitarism so that therapy can be initiated as soon as possible. Suppression tests may be performed to help identify if GH production is being suppressed by high blood sugar. Challenge or stimulation tests are generally used to detect GH deficiency and are more informative. Much controversy surrounds the use of GH stimulation tests, and the diagnosis should be considered in the context of the clinical picture.

Normal Findings ⬆ ⬇

Men: <5 ng/mL or <226 pmol/L

Women: <10 ng/mL or <452 pmol/L

Children: 0–20 ng/mL or 0–904 pmol/L

Newborns: 5–40 ng/mL or 226–1808 pmol/L

Stimulation test (using arginine, glucagon, or insulin):

Suppression test (using 100 g of glucose):

Procedure ⬆ ⬇

  1. Obtain a 5-mL venous blood sample (red-topped tube) from a fasting patient. Serum is best to use. Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

  2. Check with your laboratory for specific challenge protocols for stimulation tests such as insulin-induced hypoglycemia, arginine transfusion, glucagon infusion, L-dopa, and propranolol with exercise.

Clinical Implications ⬆ ⬇

  1. Increased hGH levels are associated with the following conditions:

    1. Pituitary gigantism

    2. Acromegaly

    3. Laron dwarfism (hGH resistant)

    4. Ectopic GH secretion

    5. Uncontrolled diabetes

  2. Decreased hGH levels are associated with the following conditions:

    1. Pituitary dwarfism

    2. Hypopituitarism

    3. Adrenocortical hyperfunction

  3. Following stimulation testing, no response (or an inadequate response) is seen in hGH and ACTH deficiencies (hypopituitarism).

    1. Blood glucose must fall to <40 mg/dL (<2.2 mmol/L).

    2. Adrenergic signs must be observed.

  4. Following suppression tests, there is incomplete or no suppression in persons with gigantism or acromegaly.

    1. Paradoxical rises in hGH may occur in patients with acromegaly.

    2. Partial suppression is sometimes seen in anorexia nervosa.

    3. In children, rebound-stimulation effect may be seen 2–5 hours following administration of ­glucose (suppression test).

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and blood-drawing procedure.

  2. Remind patient that fasting from food for 8–10 hours is required; water is permitted. For accurate levels, the patient should be free of stress and at complete rest in a quiet environment for at least 30 minutes before specimen collection.

  3. Note the patient’s physiologic state (e.g., feeding, fasting, sleep, activity) at testing in the healthcare record.

  4. For stimulation tests, collect one tube before stimulation and at timed intervals (e.g., 10, 20, 30, 45, and 60 minutes) after stimulation. For suppression tests, collect one tube before suppression and 30, 60, 90, and 120 minutes after suppression.

  5. For initial testing of hGH deficiency, a vigorous exercise test is considered to be a simple, risk-free screening test, especially for children.

  6. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Have patient resume normal activities.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. A glucose challenge test may be indicated for follow-up.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. Increased levels are associated with the use of oral contraceptives, estrogens, arginine, glucagon, L-dopa, low glucose, and insulin.

  2. Levels will rise to 15 times normal by the second day of starvation; levels also rise after deep sleep, stress, exercise, and anorexia.

  3. Decreased levels are associated with obesity and the use of corticosteroids.

  4. Many drugs interfere with test results (see Appendix E).

  5. Recently administered radioisotopes interfere with test results.