Long ACTH Test (Long Tetracosactrin Test)

 

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.

 

Testing:

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

(2) Serum or urine creatinine.

 

Baseline Steroids	Increase After ACTH	Interpretation
normal	increase 2-5 fold	normal
low	no or minimal increase	primary adrenal failure
low	no or minimal increase	congenital adrenal hyperplasia
low	large increase, may show stairstep pattern	pituitary insufficiency (secondary adrenal failure)