Which statement regarding the diagnosis of Addison's disease is accurate?

The statement about how primary and secondary Addison's disease can often be differentiated by plasma ACTH is accurate because it highlights a fundamental aspect of the pathophysiology of adrenal insufficiency. In primary adrenal insufficiency, characterized by Addison's disease, the adrenal glands are damaged and unable to produce adequate steroid hormones, leading to elevated levels of ACTH as a response from the pituitary gland. This is due to a lack of feedback inhibition on ACTH secretion.

Conversely, in secondary adrenal insufficiency (which can occur due to problems with the pituitary or hypothalamus), there is insufficient ACTH production, leading to lower ACTH levels. Thus, measuring plasma ACTH levels can effectively distinguish between the two conditions: elevated in primary Addison's disease and low in secondary adrenal insufficiency. This differentiation is clinically significant because it affects treatment approaches and helps pinpoint the underlying cause of the adrenal insufficiency.