Diagnose adrenal insufficiency.
- Administer 250 μg iv corticotropin.
- Measure serum cortisol at 30 or 60 min.
Peak cortisol < 500 nmol/L indicates adrenal insufficiency. For secondary adrenal insufficiency: specificity 95% & sensitivity 57%. Garber 2003
The test cannot rule out secondary (central) adrenal insufficiency in the first four weeks after surgery or an apoplexy event. In this early phase, the adrenal glands will continue to respond appropriately to exogenous ACTH administration. However, after four weeks of lack of ACTH, the adrenal glands become atrophic and the test becomes abnormal even in secondary adrenal insufficiency. Courtney 2004
Testing needs to be done 18-24 hours after the last dose of hydrocortisone or longer for synthetic steroids. Fleseriu 2016
Peak cortisol cutoff is assay dependent. Consider speaking with your biochemist if you’re unsure about the cortisol assay being used in your testing centre.
Total cortisol levels are affected by cortisol binding globulin levels (CBG):
|Increased CBG||Decreased CBG|
|Estrogen containing OCPs||Nephrotic syndrome|
|Immediate post-operative period|
The Endocrine Society guidelines recommend a morning cortisol (8-9 am) is used as a first line test with the following cutoffs:
- > 415 nmol/L rules out AI
- < 80 indicates AI
- 80-415 nmol/L should be investigated with an ACTH stimulation test.