Adrenocorticotropic Hormone (ACTH, Corticotropin)

Test Description

In response to a stimulus such as stress, the hypothalamus secretes corticotropinreleasing

hormone. This hormone stimulates the secretion of adrenocorticotropic

hormone (ACTH) by the anterior pituitary gland. ACTH, in turn, causes the adrenal

cortex to release the glucocorticoid hormone cortisol. As levels of cortisol in the

blood rise, the pituitary gland is stimulated to decrease ACTH production via a negative

feedback mechanism. (See Appendix B for description of hormonal feedback process).

Diurnal variations in ACTH levels occur, with peak levels occurring between 6

and 8 AM and trough levels occurring between 6 and 11 PM. Trough levels are

approximately one-half to two-thirds the peak levels.

Assessment of ACTH levels is used in conjunction with knowledge of cortisol

levels to evaluate adrenal cortical dysfunction. For example, consider the patient

with Addison’s disease in which the adrenal cortex is hypoactive, thus producing

abnormally low levels of cortisol in the blood. The anterior pituitary gland senses

the low serum cortisol levels and, as a result, increases its release of ACTH. This is

an attempt to stimulate the adrenal gland to increase its production of cortisol.

Thus, the combination of high ACTH and low cortisol levels indicates adrenocortical

hypoactivity. Conversely, if the adrenal gland is overproducing cortisol, as in the

presence of an adrenal tumor, the ACTH level will be low as the anterior pituitary

gland responds to the elevated cortisol level. Should there be a high level of ACTH

due to a pituitary tumor or a nonendocrine ACTH-producing tumor, there will also

be an elevated cortisol level, as the adrenal gland responds to stimulation by the

ACTH.

Normal Values

    6.0–76.0 pg/mL (1.3–16.7 pmol/L SI units)

Possible Meanings of Abnormal Values 

Increased                                                              Decreased                                              

Addison’s disease                                                  Cushing’s syndrome

Ectopic ACTH syndrome                                      Hypopituitarism

Pituitary adenoma                                                  Primary adrenocortical hyperfunction (tumor)

Pituitary Cushing’s disease                                    Secondary hypoadrenalism

Primary adrenal insufficiency

Stress

Contributing Factors to Abnormal Values

• Levels of ACTH may vary with exercise, sleep, and stress.

• Testing for ACTH should be scheduled no sooner than 1 week after any diagnostic

tests using radioactive materials.

• Drugs that may decreaseACTH levels: amphetamines, calcium gluconate, corticosteroids,

estrogens, ethanol, lithium carbonate, spironolactone.

Interventions/Implications

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.

Usually one morning sample is drawn, but when ACTH hypersecretion is suggested, a

second sample is drawn in the evening.

• The patient should consume a low-carbohydrate diet for 48 hours before the test.

• Fasting and limited physical activity for 10 to 12 hours before the test is required.

Procedure

• A 7-mL blood sample is drawn in either a plastic tube (because ACTH may adhere to

glass), a collection tube containing heparin, or a collection tube containing EDTA.

• Gloves are worn throughout the procedure.

Post test

• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued

  bleeding.

• The sample is to be placed on ice, labeled, and taken to the laboratory immediately.

• Report abnormal findings to the primary care provider.