Investigation of Addison's.
Normal results do not exclude Addison's and a
short synacthen test may be required.
Investigation of Cushing's.
Normal results do not exclude Cushing's and a
dexamethasone suppression test may be required.
Cortisol secretion is closely
regulated by ACTH, which is secreted in an episodic manner
superimposed on a circadian rhythm. Cortisol secretion
occurs in parallel to the secretion of ACTH. Cortisol
secretion is low in the evening and continues to decline
into the first few hours of sleep, after which there is an
increase. After waking, an individual’s cortisol secretion
gradually declines throughout the day, with fewer secretory
episodes of smaller magnitude. ACTH (and thus cortisol)
secretion is stimulated by stress.
Please note that hydrocortisone,
methylprednisolone, or prednisolone all cross-react with the