This assay is used to determine the cause of Hypocortisolism & Hypercortisolism states. In a patient with hypocortisolism, an elevated ACTH indicates Primary adrenal insufficiency whereas normal levels are consistent with secondary adranal insufficiency from pituitary or hypothalamic causes. In a patient of hypercortisolism (Cushing’s syndrome), a suppressed value is consistent with Cortisol producing Adrenal adenoma/carcinoma, Primary adrenal micronodular hyperplasia & Exogenous corticosteroid use.