Which test is used to rule out Addison's disease in the stepwise evaluation?

• A. Baseline cortisol or ACTH stimulation test
• B. CBC
• C. Urinalysis
• D. Abdominal ultrasound

Answer: (A)

In evaluating suspected Addison’s disease, you start with a screening of adrenal function. A morning baseline cortisol level can often rule out Addison’s if it’s clearly normal, since a normal value makes adrenal insufficiency unlikely in a stable patient. If the baseline result is low or unclear, the next step is the ACTH stimulation test (cosyntropin test), which directly tests adrenal reserve by measuring how well the adrenal cortex responds to synthetic ACTH. A normal cortisol rise after ACTH essentially rules out Addison’s disease, while an inadequate rise confirms adrenal insufficiency.

The other tests—CBC, urinalysis, or abdominal ultrasound—don’t assess adrenal function directly, so they aren’t used to rule out Addison’s disease in the stepwise evaluation.