ACTH

Anterior pituitary peptide from POMC that stimulates the adrenal cortex (zona fasciculata/reticularis) to make cortisol (and adrenal androgens).

• Key switch in hypercortisolism work‑ups (pituitary vs ectopic) and in adrenal insufficiency. Also explains steroid‑induced adrenal suppression.

• Diurnal: high in early morning, low at night
• ↑ACTH + ↑cortisol → Cushing disease (pituitary) or ectopic ACTH
• ↓ACTH + ↓cortisol → secondary (pituitary) adrenal insufficiency
• ↓ACTH + ↑cortisol → adrenal tumor or exogenous steroids

1. If adrenal insufficiency suspected → 8am cortisol ± ACTH stim test
2. Hypercortisolism: start with overnight dexamethasone suppression
3. If cortisol not suppressed → measure ACTH; then high‑dose dex or inferior petrosal sinus sampling if needed

1. Treat the cause: pituitary surgery for Cushing disease; tumor management for ectopic ACTH
2. Secondary adrenal insufficiency: physiologic glucocorticoid replacement; stress‑dose when ill
3. Never stop chronic steroids abruptly—taper

• Primary adrenal failure → ↑ACTH, hyperpigmentation, hyperkalemia
• Exogenous steroids suppress ACTH → adrenal atrophy
• Check meds that alter cortisol assays (e.g., OCPs) before interpreting

• Adrenal crisis: hypotension, hyponatremia, shock after stress/illness—give stress‑dose steroids immediately

1. Suspect cortisol disorder → screen (overnight 1 mg dexamethasone OR late‑night salivary cortisol OR 24‑hr urine cortisol)
2. If positive → measure ACTH
3. High ACTH → pituitary vs ectopic: high‑dose dexamethasone; consider IPSS
4. Low/undetectable ACTH → adrenal cause (image adrenals)
5. Suspect adrenal insufficiency → 8am cortisol ± ACTH stimulation test

• Skin hyperpigmentation + hypotension after illness → ↑ACTH
• Smoker with weight loss + severe hypokalemia; no suppression with high‑dose dex → ectopic ACTH
• Long‑term prednisone stopped abruptly → low ACTH & cortisol