Confirmation of the diagnosis of Addison's disease is normally made either by measuring early morning plasma levels of cortisol and ACTH, or by determining the plasma cortisol responsiveness to ACTH stimulation.
Measurement of early morning basal cortisol alone is not satisfactory in confirming Addison's disease as it is often in the normal 0900 reference range; however, in Addison's disease, this will be associated with an inappropriately high plasma ACTH level (i.e. above the normal 0900 reference range of 2.3ΓÇô18pmol/l (10ΓÇô80ng/l)).
