For suspected adrenal insufficiency, which initial test is commonly used?

• A. Hyperparathyroidism
• B. Adrenal insufficiency
• C. Cushing disease
• D. Hypothyroidism

Answer: (B)

The first step when adrenal insufficiency is suspected is a morning serum cortisol level. Cortisol is highest in the early morning, so a low reading can strongly suggest insufficient adrenal function and prompt further testing. If the morning cortisol is clearly low, an ACTH stimulation (cosyntropin) test is used to confirm the diagnosis and to distinguish between primary and secondary adrenal insufficiency. If the morning cortisol is sufficiently high, adrenal insufficiency is unlikely and no further testing is usually needed. When results are intermediate, the ACTH stimulation test helps clarify the diagnosis: a poor cortisol rise after ACTH supports adrenal insufficiency, with patterns helping differentiate whether the problem is primary (high ACTH with poor cortisol response) or secondary (low or inappropriately normal ACTH with a blunted response). In an urgent or suspected adrenal crisis, treatment with hydrocortisone may be started while testing proceeds.