Establishment of reference values for endocrine tests. I: Cushing's syndrome

Background: For diagnostic tests used in the evaluation of patients with Gu shing's syndrome, well defined reference values were lacking in our laborat ory. In the present study, we established reference values based upon test results of 50 subjects recruited from the general population. Methods: We studied 50 subjects not suspected of having Gushing's syndrome, equally distributed according to sex and age between 20 and 69 years. In a ddition to 24 h urinary excretion of free cortisol for two days, a low-dose (1 mg) overnight dexamethasone suppression test, a corticotropin releasing hormone stimulation test (CRH test) and a high-dose (7 mg) intravenous dex amethasone suppression test were performed. Reference values are given as t he observed range. Results: There was considerable intra-subject variation in 24 h urinary cor tisol excretion which could not be merely attributed to incompleteness of t he urine collection. The following reference values were established: 24 h urinary free cortisol excretion: 15-145 nmol/24 h; overnight dexamethasone suppression test: cortisol on day 2 < 50-230 nmol/l; CRH test: cortisol inc rease 15-289%, ACTH increase 36 -12.100%; high-dose, intravenous dexamethas one suppression test: cortisol after 7 h < 50-97 nmol/l; cortisol after 24 h < 50-50 nmol/l. There were no significant effects of age on any of the pa rameters studied. Apart from higher basal ACTH plasma concentrations in men , no sex differences were observed. Conclusion: We established reference values for tests that can be useful in the evaluation of patients with possible Gushing's syndrome. (C) 1998 Else vier Science B.V. All rights reserved.