ACTH Stimulation Test
A diagnostic test for adrenal insufficiency where cosyntropin (synthetic ACTH fragment) is injected and cortisol response is measured. A normal adrenal gland produces a significant cortisol rise; failure to respond suggests adrenal insufficiency. This is one of the most common diagnostic uses of a peptide drug.
Technical Context
Standard test (high-dose): 250μg cosyntropin IV or IM → serum cortisol at 0, 30, 60 minutes. Normal response: cortisol ≥18-20 μg/dL (500-550 nmol/L) at 30 or 60 minutes. Subnormal response indicates adrenal insufficiency. Low-dose test: 1μg cosyntropin IV → may be more sensitive for detecting mild/early secondary adrenal insufficiency (subtle ACTH deficiency from recent pituitary surgery or gradual glucocorticoid withdrawal). Limitations: the standard 250μg dose is supraphysiological (pharmacological rather than physiological stimulation), which may overcome mild adrenal insufficiency — hence the low-dose alternative. Timing considerations: for secondary adrenal insufficiency (pituitary/hypothalamic cause), adrenal atrophy from prolonged ACTH deficiency takes weeks-months to develop, so the ACTH stimulation test may be falsely normal in acute pituitary damage (within 2-4 weeks). The insulin tolerance test remains the gold standard for secondary adrenal insufficiency but carries hypoglycaemia risks.