Dynamic evaluation of adrenal hypofunction.
The diagnosis of adrenal hypofunction is suggested by clinical features and confirmed by biochemical testing. The characteristic features of acute primary adrenal insufficiency include orthostatic hypotension, fever, and hypoglycemia. By contrast, patients with chronic primary adrenal insufficiency have a longer history of malaise, as well as fatigue, anorexia, diarrhea, weight loss, joint and back pain, and darkening of the skin. While the clinical presentation of secondary adrenal insufficiency is similar to that of primary adrenal insufficiency, there is no hyperpigmentation, and hypotension and orthostasis are less pronounced. As a result, patients often present with vague, non-specific symptoms and the diagnosis may not be entertained. There is considerable debate regarding the best dynamic test for the diagnosis of adrenal hypofunction. Optimally, a screening test would be economic, convenient and safe. It would have high sensitivity and specificity based on consensus criteria for interpretation. Unfortunately, to date no test meets all of these criteria. Measurement of basal cortisol is an inexpensive and convenient screening test that can include (< 3 microg/dl; 83 nmol/l) or exclude (> 19 microg/dl; 524 nmol/l) adrenal insufficiency. However, most patients will have intermediate values and will require dynamic testing. This review discusses the use of metyrapone, insulin, CRH and synthetic ACTH 1-24 as provocative agents for cortisol secretion. Although the insulin and metyrapone stimulation tests have the advantage of testing the entire hypothalamic-pituitary-adrenal axis, they are cumbersome and carry more risk than the other tests. The 250 microg ACTH test works well to identify primary adrenal hypofunction, but can only detect secondary adrenal hypofunction when there is sufficient time for the glands to atrophy because of reduced endogenous ACTH stimulation. The 1 microg ACTH test has been advocated in the setting of possible secondary adrenal insufficiency, but its widespread use has been mitigated by the lack of a commercial preparation of this small dose and controversy regarding diagnostic criteria. Ultimately, the choice of test should be individualized for each patient, with knowledge of the available reference assays and the vagaries of each test.