Synonyms: Adrenocorticotrophic hormone, corticotrophin
Clinical significance
Adrenocorticotrophic hormone (ACTH) is a polypeptide hormone that exists mainly as a chain of 39 amino acids, with a molecular weight of about 4,500 daltons. It is produced in the pituitary gland and stimulates the production of steroids by the adrenal cortex. ACTH secretion is controlled at the level of the hypothalamus by corticotrophin-releasing factor (CRF) and by cortisol through negative feedback.
High values are found in Cushing’s disease, ectopic ACTH production and Addison’s disease.
Low values are found in adrenal tumours and hypopituitarism.
Clinical indications
Cushing’s disease, Cushing’s syndrome, Addison’s disease, secondary adrenal insufficiency, hypopituitarism.
Sample type
The patient must have a blood sample taken
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.
Notes
ACTH levels have a marked circadian rhythm (lowest levels between 9 and 10 pm, highest between 6 and 8 am). For this reason it is important to standardise the time of the blood sample.
Insulin, amphetamines, levodopa, metoclopramide and RU 486 can raise ACTH levels.
ACTH secretion can be increased by stress.
Dexamethasone, prednisone, hydrocortisone, prednisolone and megestrol acetate can lower ACTH levels.