Synacthen stimulation test

5 mL blood in EDTA for cortisol and possible ACTH assays, prior to a dose of 250 µg aqueous Synacthen given by IMI.

Further samples are collected at 30 and 60 minutes: 5 mL blood in plain, lithium heparin or EDTA tube for cortisol.

Plasma cortisol: a baseline (pre-Synacthen) or Post-Synacthen cortisol of >550 nmol/L or more excludes adrenal atrophy indicating a normal response, but does not necessarily indicate that there will be an adequate cortisol response to severe stress.

Failure to respond indicates adrenal insufficiency.

If basal ACTH is elevated this suggests primary adrenal failure.

Rarely, the test may be done after 3 days of priming the adrenal cortex with 1 mg depot Synacthen daily. This allows differentiation between primary adrenocortical failure (no response) and secondary adrenocortical failure.