This test is used to diagnose or exclude primary and secondary adrenal insufficiency, Addison's disease, and related conditions.[1] In addition to quantifying adrenal insufficiency, the test can distinguish whether the cause is adrenal (low cortisol and aldosterone production) or pituitary (low ACTH production).[2] The Insulin tolerance test is recognized as the gold standard assay of adrenal insufficiency, but due to the cumbersome requirement for a two-hour test and the risks of seizures or myocardial infarction, the ACTH stimulation test is commonly used as an easier, safer, though not as accurate, alternative.[7] The test is extremely sensitive (97% at 95% specificity) to primary adrenal insufficiency, but less so to secondary adrenal insufficiency (57-61% at 95% specificity); while secondary adrenal insufficiency may thus be dismissed by some interpreters on the basis of the test, additional testing may be called for if probability of secondary adrenal insufficiency is particularly high.[1]