Rapid ACTH stimulation test

The unstimulated serum cortisol and rapid ACTH stimulation tests are useful in the diagnosis of adrenal crisis (Table 42-2). The insulin tolerance test is contraindicated owing to preexisting hypoglycemia. The metyrapone test is also contraindicated because metyrapone inhibits cortisol production. 

Addison s disease will have an abnormal response to the rapid ACTH-stimulation test. Plasma ACTH levels are usually 400 to 2000 pg/mL in primary insufficiency, versus normal to low (0 to 50 pg/mL see Table 74-3) in secondary insufficiency. A normal cosyntropin-stimulation test does not rule out secondary adrenal insufficiency. 

ACTH stimulation of the adrenals will fail to elicit an appropriate response in states of adrenal insufficiency. A rapid test for ruling out adrenal insufficiency employs cosyntropin (see below). Plasma cortisol levels are measured before and either 30 minutes or 60 minutes following an intramuscular or intravenous injection of 0.25 mg of cosyntropin. A normal plasma cortisol response is a stimulated peak level exceeding 20 g/dL. A subnormal response indicates primary or secondary adrenocortical insufficiency that can be differentiated using endogenous plasma ACTH levels (which are increased in primary adrenal insufficiency and decreased in the secondary form). 

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