The ACTH stimulation test is a test of the function of the adrenal glands, usually when Addison's disease or a similar condition is suspected. The patient is given a small dose of ACTH (which is normally produced by the pituitary gland) or a similar hormone. The patient's cortisol levels are then measured at regular intervals in the following hour although to distinguish between conditions the test can last up to 48 hours. In either case, a baseline ACTH level should be established as well, although test results for this hormone tend to be inaccurate. High ACTH levels also point to a problem with the adrenals, but low levels often point to a problem with the pituitary.