ACTH, Plasma

Adrenocorticotropic Hormone (ACTH) is produced by the pituitary gland to stimulate the adrenal cortex to release cortisol. Measuring ACTH helps differentiate between primary adrenal insufficiency (Addison's disease, high ACTH, low cortisol) and secondary adrenal insufficiency (pituitary issue, low/normal ACTH, low cortisol), or Cushing's disease (pituitary tumor secreting excess ACTH) versus other causes of high cortisol. Levels follow a diurnal rhythm, highest in the early morning.