Which diagnostic test is the most helpful in distinguishing primary from secondary adrenocortical insufficiency?

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Cosyntropin (Cortrosyn) is a synthetic form of adrenocorticotropic hormone (ACTH) that stimulates the adrenal glands to produce cortisol. In primary adrenal insufficiency (Addison's disease), the adrenal glands do not respond to ACTH stimulation, while in secondary adrenal insufficiency, cortisol production is impaired due to decreased ACTH secretion from the pituitary gland. Therefore, a cosyntropin stimulation test can help to differentiate between primary and secondary adrenal insufficiency. MRI and CT scans may reveal structural abnormalities in the adrenal gland, but they do not differentiate between primary and secondary insufficiency. Dexamethasone suppression tests are used to diagnose Cushing's syndrome, not adrenal insufficiency.

Which Diagnostic Test Is the Most Helpful in Distinguishing Primary