Improved specificity of a new direct assay for urinary cortisol: application in corticoid treated patients

Twenty four hours urinary free cortisol (UFC) excretion has been determined in 35 eucortisolic control patients, in seven of them before and after tetracosactide (Synacthen) stimulation and in 18 patients treated by anti-inflammatory steroids. Results of the new direct Immunotech RIA (DIm) were compared to those of the INCSTAR RIA kit with (ECA) or without methylene chloride extraction (DCA). In controls DIm UFC (106.2+/-45.8 nmol/24h) was significantly lower than DCA UFC (397+/-119 nmol/24h) and than ECA UFC (127+/-49 nmol/24h). After tetracosactide stimulation, median of DCA/DIm ratio decreased from 3.61 to 1.88 whereas ECA/DIm ratio did not change significantly (1.31 to 1.06). In treated patients most DCA and ECA results were over the upper limit of controls but only 5 DIm results were increased. DIm assay showed good specificity and practicability and may be used with benefit in the evaluation of the adrenal gland function.