Cortisol is a naturally occurring hormone that is secreted by the adrenal glands. In conditions of extreme stress where the body goes into a “fight or flight” state, cortisol is secreted along with adrenalin. This secretion of cortisol is controlled by another hormone produced in the pituitary gland, called ACTH (adrenocorticotropic hormone). Cortisol itself plays many vital roles in the body, including blood pressure control, immune system regulations, and digestion of protein, glucose, and lipids. However, an excess of cortisol can lead to high blood pressure, obesity, increased blood glucose levels, muscle weakness, osteoporosis (weak bones), irregular menses, and delayed development in children. An ACTH stimulation test can help to diagnose whether abnormal cortisol levels are due to a problem with the adrenal gland or with the pituitary gland. Typically, this test involves taking blood samples for testing, though some cases may also require a saliva and urine analysis.
A cortisol depression test is usually ordered when a patient shows symptoms of Cushing's syndrome, such as obesity and muscle degeneration, or Addison's disease, such as fatigue and increased pigmentation. In cases of excess cortisol, a dexamethadosone suppression test can help to determine if the reason is an increased production of ACTH. The ACTH stimulation test can help with cases of low cortisol. The adrenal glands are stimulated with an excess of ACTH and if they respond by producing additional cortisol, the problem is probably due to low levels of ACTH. If there is no significant rise in cortisol levels, the problem is with the adrenal glands.
Under normal circumstances, cortisol levels are lowest at bedtime and highest first thing in the morning. Therefore, blood required for the ACTH test will probably be drawn first at around 8 am, followed by another sample at around 4 pm. You may have to fast for around 6 hours before the first blood sample is drawn and have a carbohydrate-rich diet around 12 hours before the test. If urine needs to be tested, you may be required to collect all urine produced during a 24-hour period prior to the test.
For the ACTH stimulation test (also known as cosyntropin stimulation test or cortrosyn stimulation test), blood samples are drawn before and after an injection of artificial ATCH. If the adrenal glands are functioning normally, they will respond to the additional ACTH by producing more cortisol. This indicates that the patient's low cortisol levels are due to impaired production of ACTH. However, if the cortisol levels do not rise significantly, the problem is with the adrenal glands.