ACTH Stimulation Tests	

A variety of ACTH stimulation tests have been described in which either ACTH1-39 or ACTH1-24 is given. Only the first 24 amino acids of ACTH are required for full biological activity. Thus, synthetic preparations such as tetracosactrin (ACTH1-24) are usually used.
However, a lack of response to tetracosactrin (Synacthen Depot) does not distinguish between primary and secondary adrenocortical insufficiency, and this can only be achieved by administering depot tetracosactrin – a zinc-adsorbed preparation with a prolonged action over approximately twenty-four hours. Where depot preparations are not available, continuous intravenous infusions of ACTH may be given.
Tetracosactrin tests in African patients with chronic pulmonary tuberculosis have shown that some 30% have an impaired cortisol response. The significance of this is unclear. 

See later:
• ‘Short’ Tetracosactrin Test
• Depot Tetracosactrin Test