Cortisol Suppression Test in Patients with Elevated Adrenocorticotropic Hormone Levels

Abstract

Increased adrenocorticotropic hormone (ACTH) levels after bilateral adrenalectomy could be secondary to a pituitary tumor, under replacement with cortisol, or an abnormality in the hypothalmic-pituitary-adrenal feedback loop. To distinguish between these possibilities, ACTH levels were measured before and after cortisol infusion (20 mg/h for 4 hours) in five groups: normal volunteers; patients with idiopathic adrenal insufficiency; and with bilateral adrenalectomy for Cushing's syndrome with no roentgenographic evidence of pituitary tumor, with pituitary tumors, and with equivocal roentgenographic studies (suspect pituitary tumors). Control ACTH levels in all groups of patients were higher than in normal volunteers but there was overlapping. Cortisol infusion suppressed ACTH in all subjects but the reductions in the last two groups were less than in the first three. The cortisol suppression test appears to be useful in determining whether increased ACTH level after adrenalectomy is due to a pituitary tumor.