An 8 AM serum cortisol level is used in diagnosing which adrenal condition?

• A. Adrenal insufficiency
• B. Cushing disease
• C. Hyperaldosteronism
• D. Addison disease

Answer: (A)

An 8 AM serum cortisol level is used to screen for adrenal insufficiency because cortisol normally peaks in the early morning. A low morning cortisol suggests the adrenal glands aren’t producing enough cortisol, pointing to adrenal insufficiency (which includes Addison disease). If the level is low, a subsequent ACTH stimulation test is done to confirm the diagnosis. In contrast, Cushing disease involves excess cortisol, so morning cortisol would not be low, and hyperaldosteronism centers on aldosterone, not cortisol. Addison disease is a form of adrenal insufficiency, so the test supports diagnosing adrenal insufficiency.