Synacthen stimulation test

Keywords: Short synacthen stimulation test

Specimen:

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

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

Method:

See Cortisol.

Reference Interval:

Plasma cortisol: a baseline (pre-Synacthen) or Post-Synacthen cortisol (cut-off is method dependent) or a an increment in serum cortisol of > 200nmol/L at 30 minutes excludes adrenal atrophy indicating a normal response, but does not necessarily indicate that there will be an adequate cortisol response to severe stress. Thresholds are very method dependent, and assessment of response should be made with appropriate method dependent thresholds.

Application:

Investigation of suspected primary or secondary adrenocortical insufficiency.

Assessment of possible adrenal suppression/atrophy due to steroid therapy.

Interpretation:

Failure to respond indicates adrenal insufficiency.

If basal ACTH is elevated together with an inadequate increment in serum sortisol, 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.

Reference:

Wallace I et al. Ann Clin Biochem 2009; 46: 351-367.

El Farhan N et al. Clin Endocrinol 2013; 78: 673-680.