Short Synacthen Test Interpretation — RACP Adult Medicine MCQ

Instant feedback + full explanation. One question, done properly.

ModerateEndocrinologyShort Synacthen Test InterpretationRACP Adult Medicine

A 30-year-old woman with suspected Addison disease has a morning cortisol of 180 nmol/L (equivocal). A short Synacthen test is performed: baseline cortisol 180 nmol/L, 30-minute cortisol 320 nmol/L. What is the interpretation?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Primary adrenal insufficiency confirmed

A 30-minute cortisol <450 nmol/L (some labs use 500 nmol/L) after 250 μg IV Synacthen (tetracosactide) confirms adrenal insufficiency. The inadequate cortisol response (320 nmol/L) indicates the adrenal glands cannot respond appropriately to ACTH stimulation. A paired ACTH level distinguishes primary (ACTH elevated) from secondary (ACTH low/normal). Anti-21-hydroxylase antibodies should be tested for primary AI.

Reference: Society for Endocrinology – 2020; eTG Endocrine 2024