Basal cortisol is predominantly used as part of dynamic testing for hyperadrenocorticism or hypoadrenocortism when paired with additional samples collected after administration of ACTH (ie. ACTH stimulation test) or dexamethasone (ie. dexamethasone suppression test). However, random cortisol can be a useful stand-alone screening test to eliminate hypoadrenocorticism/Addison’s disease from a differential list. Typically if basal cortisol concentrations are above 60 nmol/L, hypoadrenocortism is very unlikely. If basal cortisol concentrations are low this neither confirms nor excludes hypoadrenocorticism, but warrants an ACTH stimulation test to fully assess the adrenal reserve.
Heparinised plasma or Serum
Heparin or plain (red top) tube