How is Addison's disease typically diagnosed?

Addison's disease, also known as primary adrenal insufficiency, is characterized by a failure of the adrenal glands to produce sufficient amounts of cortisol and often aldosterone. When diagnosing this condition, one key physiological response involves measuring levels of cortisol and adrenocorticotropic hormone (ACTH) in the blood.

In Addison's disease, the adrenal glands are damaged and unable to produce adequate cortisol, which leads to low plasma cortisol levels. As a compensatory mechanism, the pituitary gland secretes increased amounts of ACTH in an attempt to stimulate the adrenal glands. Therefore, a typical diagnostic finding for Addison's disease includes decreased plasma cortisol levels alongside elevated ACTH levels.

This pattern distinguishes Addison's disease from other forms of adrenal insufficiency, such as secondary adrenal insufficiency, where the adrenal glands are functional but are not being adequately stimulated by ACTH due to a lack of pituitary hormone production. In that case, you would expect low levels of both cortisol and ACTH.

Thus, the combination of decreased plasma cortisol and elevated ACTH is a hallmark of Addison's disease, making this answer correct in the context of diagnosis.