The diagnostic value of hypothalamic-pituitary-adrenocortical function tests in patients with Cushing's syndrome

The following examinations, including the estimation of urinary neutral steroid metabolites, plasma cortisol, the percentage of unbound-cortisol, cortisol production rate, plasma adrenocorticotrophin (ACTH), dexamethasone suppression test, ACTH stimulation test, metopirone test, lysine-vasopressin (LVP) test and insulin tolerance test, were conducted in 16 patients with Cushing's syndrome for the presence of hypercoticism and for identifying the cause of this syndrome. Of these tests, the measurements of plasma cortisol late in the day and single dose dexamethasone suppression test were most useful for the diagnosis of hypercorticism because of their reliability and simplicity. Urinary 17-KGS, THF/THE ratio, cortisol production rate and low dose dexamethasone suppression test were also useful, whereas insulin test and LVP test were less valuable for this purpose. For the identification of the causes of this syndrome, lysine vasopressin test and metopirone test were most reliable, and plasma ACTH was also useful for this purpose, whereas insulin test and ACTH stimulation test were less valuable.