ACTH is a blood test that measures cortisol (steroid) levels, and is used to diagnose diseases that affect the function of the pituitary gland, which releases ACTH to stimulate the adrenal glands to release cortisol. Low cortisol levels are seen in Addison's disease, while high levels of cortisol are seen in Cushing's syndrome.
ACTH levels vary during the day, with higher amounts produced in the morning between 4-8 am, and lower amounts produced at night between 8-10 pm. This variation can be affected by stress, disease, or cancer.
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