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 taken: high in the early morning and low in the evening. Cortisol levels are interpreted based on the sample collection time (AM or PM), the presence of corticosteroid-containing medications, etc. Urine cortisol levels, expressed in nanomoles per litre or nanomoles per day (nmol/L or nmol/d), are sometimes useful in confirming ambiguous blood results.
Above-normal levels of urine cortisol generally indicate overactive adrenal glands (Cushing’s syndrome) possibly due to hyperstimulation by ACTH (problem with the pituitary gland) or uncontrolled adrenal gland function (hyperplasia or tumour). Low urine cortisol levels can be the result of corticosteroid treatment (not detected by the test), hypoactive adrenal glands (Addison’s disease), 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).