The adrenal gland makes many different hormones and is divided into two distinct zones: the medulla and the cortex. The medulla makes hormones called catecholamines, such as adrenaline. The cortex primarily makes the hormones cortisol and aldosterone. Diseases of the adrenal gland can often be diagnosed with blood tests that measure the levels of these different hormones, although most adrenal gland disorders affect only the adrenal cortex.
Blood cortisol is one of the basic tests used to assess adrenal gland function. Cortisol levels rise and fall throughout the day, so a single blood sample may not be effective at diagnosing a deficiency or overproduction. As a result, multiple samples may be taken. Cortisol levels can also be measured before or after stimulation of the adrenal gland to get a better sense of adrenal function.
Adrenocorticotropin hormone, or ACTH, is a hormone made by the pituitary gland that stimulates the adrenal glands to make cortisol. As a result, it can be measured to assess adrenal function. If the adrenal glands are not working effectively, the pituitary secretes more ACTH to stimulate them to make more cortisol. As a result, people with poorly functioning adrenal glands typically have elevated ACTH levels.
Adrenal Stimulation Test
Another way to more accurately measure adrenal gland function is to measure cortisol levels before and after stimulation of the adrenal glands. For this test, the cortisol level is measured and then the patient is injected with a synthetic form of ACTH called cosyntropin. After 45 minutes, the blood cortisol level is measured again to see if the adrenal glands produced more cortisol in response to the cosyntropin. Failure of the blood cortisol levels to rise suggests adrenal gland malfunction.
The corticotropin-releasing hormone test can also be used to test adrenal gland function. First, baseline levels of ACTH and cortisol are measured. Then, corticotropin-releasing hormone -- a chemical that stimulates the release of ACTH -- is injected. Cortisol and ACTH levels are measured every 15 minutes. Typically, ACTH levels peak after 15 to 30 minutes, and cortisol levels peak 30 to 40 minutes after the injection of corticotropin-releasing hormone. Failure of cortisol levels to rise after an increase in ACTH suggests adrenal failure.