Which finding would be expected if cortisol fails to rise after cosyntropin stimulation?

• A. Cortisol fails to rise after cosyntropin stimulation
• B. Cortisol rises normally after cosyntropin
• C. Cortisol decreases after cosyntropin
• D. Cosyntropin is contraindicated

Answer: (A)

The key idea is adrenal reserve: cosyntropin (synthetic ACTH) should stimulate the adrenal cortex to release cortisol. If cortisol does not rise after administration, it means the adrenal cortex cannot respond to ACTH—i.e., adrenal insufficiency. This suggests impaired adrenal cortex function, which can be due to primary adrenal disease (adrenal destruction) or, after long-standing ACTH deficiency, secondary/tertiary disease where the adrenals have atrophied. Clinically, you’d expect a blunted or absent cortisol increase after stimulation, with typical laboratory thresholds showing a peak cortisol that remains below the normal post-stimulation level (varying by lab, often not reaching around 18 µg/dL, or a rise of less than ~7–9 µg/dL from baseline).