🩺 ACTH Stimulation Test (Cosyntropin) Simulator

Baseline Cortisol — The Starting Point Before Stimulation

A morning blood draw sets the reference cortisol level for comparison.

• 6–23: Normal AM cortisol (mcg/dL, wide morning range)
• 8 AM: Sample timing (cortisol peaks diurnally)
• Serum: Draw type (single venous blood tube)
• Reference: Purpose (compares to post-stim value)

Why a baseline draw matters

Establishes each patient's own starting point for comparison.

Diurnal cortisol rhythm

Cortisol naturally peaks near waking, so timing matters.

Cosyntropin — Synthetic ACTH as a Direct Adrenal Challenge

Cosyntropin mimics ACTH, directly asking the adrenal cortex to respond.

• 250 mcg: Standard dose (IV or IM injection)
• ACTH 1–24: Drug identity (synthetic fragment of ACTH)
• Minutes: Onset (rapid adrenal receptor binding)
• 30 & 60 min: Sampling (post-injection cortisol draws)

What cosyntropin does

Synthetic ACTH binds adrenal receptors, bypassing the pituitary.

Why bypass the pituitary

Isolates the adrenal gland itself as the test subject.

Healthy Adrenal Cortex — A Vigorous Cortisol Surge

Intact cortical cells answer ACTH with a strong, rapid cortisol rise.

• >18: Peak cortisol (mcg/dL typical pass threshold)
• 30–60 min: Time to peak (post-cosyntropin)
• >7: Rise magnitude (mcg/dL above baseline)
• Intact: Cell status (zona fasciculata fully functional)

Cellular machinery at work

Steroidogenic cells convert cholesterol to cortisol on demand.

Reading a normal result

A brisk rise proves the gland can still respond.

Addison's Disease — A Gland That Cannot Answer the Call

Autoimmune-destroyed cortex tissue cannot make more cortisol, ACTH or not.

• <18: Peak cortisol (mcg/dL — blunted response)
• Autoimmune: Common cause (~80% of primary cases)
• >90%: Cortex destroyed (before symptoms typically appear)
• High: ACTH level (pituitary compensates, gland can't)

Why stimulation fails

Destroyed tissue simply has no cells left to respond.

Primary vs secondary clue

High baseline ACTH plus no response points to the gland.

Diagnostic Outcome — Confirming Primary Adrenal Insufficiency

An inadequate cortisol rise confirms the problem sits at the adrenal gland.

• ≥18 mcg/dL: Pass threshold (peak cortisol, common cutoff)
• Addison's: Fail result (primary adrenal insufficiency)
• Hormone Rx: Next step (lifelong glucocorticoid replacement)
• High: Test accuracy (gold-standard adrenal function test)

Interpreting the final result

Peak below threshold means the gland itself has failed.

What happens next

Confirmed patients start lifelong glucocorticoid replacement therapy.