Adrenal function testing

Glucocorticoid stimulation and suppression tests are essential to the definitive diagnosis of diseases of the hypothalamic-pituitary-adrenal axis, because they document abnormal physiologic control of hormonal secretion. Similarly, diseases of the renin-angiotensin-aldosterone axis are diagnosed by mineralocorticoid stimulation and suppression testing. [Ed. Note: See Moore TJ, Williams GH: Adrenal causes of hypertension, in this issue.] Unlike tests of glucocorticoid function, testing of the renin-angiotension-aldosterone system is more complicated, because knowledge of posture and dietary sodium are necessary to interpret the results. However, measurement of the tropic hormone renin and plasma levels of aldosterone can be accurately made, allowing precise definition of this system. Errors are most commonly encountered when dynamic tests of cortisol output are performed in patients taking medications that may interfere with the assays or with the metabolism of the administered compounds, such as dexamethasone or metyrapone. Abnormal, spurious values may also be obtained in some individuals who do not have adrenocortical hyperfunction if they are very obese or if testing is performed in a setting of clinical stress. Careful attention to these pitfalls will avoid errors and allow the clinician to arrive at the correct diagnosis.