Cortisol is produced by the adrenal glands in response to ACTH stimulation from the pituitary gland. Cortisol is an essential hormone in stress situations (disease, surgery, hypoglycemia, etc.). However, too much cortisol is harmful to the body (suppresses the immune response, etc.). Cortisol levels vary depending on the time of day when the sample is collected: high in the early morning and low in the evening. Cortisol levels are interpreted based on the sample collection time (AM or PM), urine cortisol and ACTH levels, and so on.
Above-normal levels of AM or PM cortisol usually indicate hyperactive adrenal glands (Cushing’s syndrome) possibly due to ACTH hyperstimulation or uncontrolled adrenal gland function. High cortisol levels are often monitored using a dexamethasone suppression test. In rare cases of Cushing’s syndrome, AM or PM cortisol levels may be reversed (PM cortisol equal to or higher than AM cortisol).
Low AM or PM cortisol levels (Addison’s disease) are indicative of either hypostimulation of the adrenal glands by ACTH (pituitary disorder), or a problem with the adrenal glands themselves (autoimmune disease, infection, cancer or other cause of gland destruction).