This test is used to distinguish primary from secondary adrenal insufficiency. It is performed over several days.


Patient Preparation:

(1) Patients can be ambulatory and eat a normal diet during testing.

(2) If a patient develops adrenal crisis, dexamethasone (20 µg/kg/day) can be given without interfering with testing.


ACTH Administration:

(1) Several protocols exist

(2) One protocol is for daily IV infusion of ACTH over several days

(3) Another uses a depot ACTH analogue (tetracosactrin).


Specimen Collection:

(1) Varies with protocol.

(2) One protocol involves collection of 24 hour urine specimens for 2 days prior to testing; ACTH is administered over 3 days with 24 hour urine specimens collected on each of the 3 days.



(1) Serum cortisol or urine glucocorticoids (17-hydroxycorticosteroids, free cortisol)

(2) Serum or urine creatinine.


Baseline Steroids

Increase After ACTH



increase 2-5 fold



no or minimal increase

primary adrenal failure


no or minimal increase

congenital adrenal hyperplasia


large increase, may show stairstep pattern

pituitary insufficiency (secondary adrenal failure)


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