This test is used to distinguish primary from secondary adrenal insufficiency. It is performed over several days.
(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.
(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).
(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.
Increase After ACTH
increase 2-5 fold
no or minimal increase
primary adrenal failure
congenital adrenal hyperplasia
large increase, may show stairstep pattern
pituitary insufficiency (secondary adrenal failure)
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Specialty: Endocrinology, Clinical Laboratory