Adrenocorticotropic hormone (ACTH) is secreted by the basophils of the adenohypophysis. ACTH stimulates the adrenal cortex to secrete (1) glucocorticoids, of which cortisol predominates; (2) adrenal androgens, which are converted by the liver to testosterone; and, to a lesser degree, (3) mineralocorticoids, of which aldosterone predominates. ACTH secretion is closely linked to melanocyte-stimulating hormone; it also is thought to stimulate pancreatic cells and the release of GH.

ACTH release, which is stimulated by its corresponding hypothalamic releasing factor, occurs episodically in relation to decreased circulating levels of glucocorticoid, increased stress, and hypoglycemia. ACTH levels also vary diurnally; the highest levels occur on awakening, decrease throughout the day, and then begin to rise again a few hours before awakening. Circulating aldosterone levels may influence ACTH secretion to some extent; however, androgens are believed to have no effect on ACTH levels. ACTH assays are expensive to perform and are not universally available.

Note: Normal values vary according to the laboratory performing the test. Results are usually evaluated in relation to other tests of adrenal-hypophyseal function (e.g., plasma cortisol).

• ACTH levels vary diurnally; highest levels occur upon awakening, decrease throughout the day, and then begin to rise again a few hours before awakening.
• Numerous drugs may lead to decreased ACTH levels (e.g., adrenocorticosteroids, estrogens, calcium gluconate, amphetamines, spironolactone, and ethanol).
• Stress, exercise, and blood glucose levels may affect results.

• Signs and symptoms of adrenocortical dysfunction:
  • Elevated ACTH levels with low cortisol levels indicate adrenocortical hypoactivity (Addison's disease).
  • Low ACTH levels with high cortisol levels indicate adrenocortical hyperactivity (Cushing's syndrome) caused by benign or malignant adrenal tumors.
  • High ACTH levels, without diurnal variation, combined with high cortisol levels indicate adrenocortical hyperfunction caused by excessive ACTH production (e.g., resulting from pituitary adenoma and nonendocrine malignant tumors in which there is ectopic ACTH production).
  • Decreased ACTH levels are associated with panhypopituitarism, hypothalamic dysfunction, and long-term adrenocorticosteroid therapy.

Nursing Care Before the Procedure

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

• For this test, the client should follow a low-carbohydrate diet for 48 hours and fast from food for 12 hours before the test.
• In addition, strenuous exercise should be avoided for 12 hours before the test, and 1 hour of bed rest is necessary immediately before the test.
• Medications that may alter test results should be withheld for at least 24 to 48 hours or longer before the study, although this practice should be confirmed with the person ordering the test.
• The client should be informed that it may be necessary to obtain more than one sample and that samples must be obtained at specific times to detect peak and trough levels of ACTH.

Between 6 and 8 AM (peak ACTH secretion time), a venipuncture is performed and the sample collected in a green-topped tube. The sample must be placed in a container of ice and sent to the laboratory immediately. When ACTH hypersecretion is suspected, a second sample may be obtained between 8 and 10 PM to determine whether diurnal variation in ACTH levels is occurring.

• The ACTH stimulation test can be conducted by the timed serial laboratory analysis of blood plasma samples for cortisol levels after the administration of metyrapone. The ACTH suppression test can be conducted by the laboratory analysis of blood plasma samples for cortisol levels after the administration of dexamethasone. The tests are performed to assist in the diagnosis of Addison's disease or Cushing's syndrome.

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 foods and any medications withheld before the test, as well as usual activities.
• Complications and precautions: Note cortisol level and its relation to increases in ACTH production by the pituitary gland.