The adrenal glands can be evaluated in several different ways and more than one of these may be required to fully understand the nature of the problem. Conventional physicians routinely test for adrenal function by measuring the levels of the adrenal hormone cortisol.
Because cortisol is secreted at different levels throughout the day (most in the morning, least around midnight), multiple samples (usually 4) should be taken through out the day at specific times. Individual samples can be taken by blood or saliva. A single serum or saliva cortisol by itself will usually not be very useful.
Alternatively, a 24-hour cumulative urine test can be done which will show how much cortisol was secreted during that period. This test, while very useful, does not reveal any information about the adrenal output at any specific time.
An ACTH (Cortrosyn) baseline and challenge may be the best tests to determine whether your adrenal glands are able to respond to signals from your brain. The pituitary may not be producing enough ACTH or – more likely – the adrenal glands may not be responding adequately to the brain's signals. Some consider two 24-hour urine samples, one before and one after the ACTH injection, to be the best method of testing for adrenal weakness.
The dexamethasone test, along with baseline measurements, is usually performed only when adrenal hyperfunction is being evaluated. It can differentiate adrenal disease (altered response to ACTH ) from pituitary disorders (altered production of ACTH).
The secretion of ACTH from the pituitary gland is normally regulated by the level of cortisol in the blood. ACTH stimulates the adrenal cortex to produce cortisol. As plasma cortisol levels increase, ACTH secretion is suppressed; as cortisol levels decrease, ACTH increases. Dexamethasone is a synthetic steroid similar to cortisol, which suppresses ACTH secretion in normal individuals. Giving dexamethasone should reduce ACTH levels resulting in decreased cortisol levels.
With or without lab testing, if symptoms indicate adrenocortical deficiency, a low dose therapeutic trial of cortisol for several weeks may prove both informative and helpful.
A 24-Hour urinary free cortisol level is the most specific diagnostic test. Levels higher than 50 to 100mcg per day for an adult suggest Cushing's syndrome. Once Cushing's syndrome has been diagnosed, other tests are used to find the exact location of the abnormality that leads to excess cortisol production. These tests could include dexamethasone suppression test, CRH stimulation test, direct visualization of the endocrine glands (radiologic imaging), petrosal sinus sampling and the dexamethasone-CRH test.
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