In primary adrenal insufficiency (Addison disease), what would be the expected cortisol level following ACTH stimulation?

In primary adrenal insufficiency (Addison disease), what would be the expected cortisol level following ACTH stimulation?

• A. Increase from baseline
• B. Decrease from baseline
• C. No change from baseline
• D. Increase briefly then fall

Answer: (C)

The key idea is that the ACTH stimulation test checks whether the adrenal cortex can mount a cortisol response to ACTH. In primary adrenal insufficiency, the adrenal glands are damaged and cannot produce cortisol effectively, so giving ACTH does not provoke a significant rise. The cortisol level after stimulation remains essentially the same as baseline, indicating a blunted or absent response. This contrasts with normal function or with secondary adrenal insufficiency, where the adrenals can respond and cortisol increases after ACTH. So a lack of change from baseline best fits Addison disease, while options suggesting an increase, a decrease, or a transient rise would not reflect the impaired adrenal reserve.

The key idea is that the ACTH stimulation test checks whether the adrenal cortex can mount a cortisol response to ACTH. In primary adrenal insufficiency, the adrenal glands are damaged and cannot produce cortisol effectively, so giving ACTH does not provoke a significant rise. The cortisol level after stimulation remains essentially the same as baseline, indicating a blunted or absent response. This contrasts with normal function or with secondary adrenal insufficiency, where the adrenals can respond and cortisol increases after ACTH. So a lack of change from baseline best fits Addison disease, while options suggesting an increase, a decrease, or a transient rise would not reflect the impaired adrenal reserve.