Growth hormone (GH, STH, SH) is secreted in episodic bursts, usually during early sleep. The effects of GH occur throughout the body. GH promotes skeletal growth by stimulating hepatic production of proteins. It also affects lipid and glucose metabolism. Under the influence of growth hormone, free fatty acids enter the circulation for use by muscle; hepatic glucose production (gluconeogenesis) also rises. Growth hormone also increases blood flow to the renal cortex and the glomerular filtration rate; the kidney excretes more calcium and less phosphate than usual. GH is believed to antagonize insulin.

Deficiencies in GH are apparent only in childhood. Children with GH deficiency have very small statures but normal body proportions. The child also may be deficient in other hypophyseal hormones, and this disorder is known as pituitary dwarfism.

Excessive levels of GH are apparent in all ages. Excess GH in children causes the long bones of the skeleton to enlarge and produces gigantism. In adults, the bones of the skull, hands, and feet thicken to produce the physical appearance of acromegaly. In this disorder, the internal organs, skeletal muscle, and heart muscle hypertrophy. Nerves and cartilage also enlarge and may produce nerve compression and joint disorders.

Note: Values may vary according to the laboratory performing the test.

• Hyperglycemia and therapy with drugs such as adrenocorticosteroids and chlorpromazine may cause falsely decreased levels.
• Hypoglycemia, physical activity, stress, and a variety of drugs (e.g., amphetamines, arginine, dopamine, levodopa, methyldopa, beta blockers, histamine, nicotinic acid, estrogens) may cause falsely elevated levels.³⁸

• Growth retardation in children with decreased levels indicative of pituitary etiology
• Monitoring for response to treatment of growth retardation caused by GH deficiency
• Suspected disorder associated with decreased GH (e.g., pituitary tumors, craniopharyngiomas, tuberculosis meningitis, and pituitary damage or trauma)
• Gigantism in children with increased levels indicative of pituitary etiology
• Support for diagnosing acromegaly in adults as indicated by elevated levels; acidophil or chromophobe tumors of the adenohypophysis may account for these elevated levels³⁹

Nursing Care Before the Procedure

Client preparation is essentially the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• The client should be informed that the test will be performed on 2 consecutive days, between the hours of 6 and 8 AM.
• The client should fast from food and avoid strenuous exercise for 12 hours before each sample is drawn.
• Additionally, it is recommended by some that the client be maintained on bed rest for 1 hour before each sample is obtained.
• Because many drugs may affect serum GH levels, a medication history should be obtained. It is recommended that those drugs that alter test results be withheld for 12 hours before the study, although this practice should be confirmed with the person ordering the test.

The test is performed on 2 consecutive days, between the hours of 6 and 8 AM. A venipuncture is performed and the sample collected in a red-topped tube. The sample should be handled gently to avoid hemolysis and sent immediately to the laboratory.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Resume food and any medications withheld before the test, as well as usual activities.
• Abnormal values: Note and report increased levels. Assess for signs and symptoms of hyperglycemia and abnormal (increased) growth pattern. Prepare client for possible surgery or radiation therapy. Note and report decreased levels in association with GH stimulation tests. Assess growth pattern abnormalities for age and gender. Instruct caretaker in availability of replacement therapy and follow-up, if appropriate.