Adrenocorticotropic Hormone (ACTH) details

Adrenocorticotropic hormone (ACTH) is released by the pituitary gland and acts as the signal that tells your adrenal glands to produce cortisol. Because ACTH and cortisol are part of the same feedback loop, testing them together — often at the same time of day, since both follow a daily rhythm — helps pinpoint the source of an abnormal cortisol result. High ACTH with high cortisol can point to a pituitary tumor producing excess ACTH (Cushing's disease); high ACTH with low cortisol suggests the adrenal glands themselves aren't responding properly (primary adrenal insufficiency, or Addison's disease); and low ACTH with low cortisol points toward a pituitary or hypothalamic problem (secondary adrenal insufficiency). This makes ACTH a key piece of working out why cortisol levels are abnormal, rather than a standalone screening test.