ACTH (Adrenocorticotropic Hormone) |
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ACTH is the pituitary hormone that stimulates production and release of cortisol by the adrenal gland. ACTH binds to cell membranes and stimulates steroidogenesis by enhancing conversion of cholesterol to pregnenolone. The major clinical use for the measurement of ACTH is to help delineate the cause of Cushing syndrome. In patients with primary adrenal disease, ACTH levels are suppressed, while in those with a pituitary tumor or ectopic ACTH producing tumor, ACTH levels are elevated. Patients with pituitary tumors usually have ACTH levels up to two times the upper limit of normal, while the majority of patients with ectopic ACTH tumors have higher levels.
In patients with primary adrenal cortical insufficiency (Addison's Disease), plasma ACTH is often strikingly elevated, usually above 250 pg/mL. In secondary adrenocortical insufficiency, plasma ACTH is depressed, usually below 50 pg/mL.
Reference range is 0 - 60 pg/mL.
Because of the diurnal variation in ACTH secretion, levels drawn at 0900 offer the best discrimination between the various forms of Cushing syndrome. Specimen requirement is two 5 mL lavender top (EDTA) tubes. Prior to collection, the tubes should be cooled in ice. Following collection, tubes should be mixed and placed immediately in an ice water bath for transport to the laboratory.
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