DEVELOPMENT OF AN ASSAY FOR URINARY FREE CORTISOL DETERMINATION ON THE TECHNICON IMMUNO-1(R) SYSTEM

Objectives: To develop and evaluate a method using an ethyl acetate ex traction procedure for the determination of urinary free cortisol on t he Technicon Immune 1(R) system from Bayer Corporation. Design and Met hods: We tested the assay precision, linearity, and correlation with t he Urinary Kallestad(TM) Quanticoat Cortisol radio immunoassay. We als o studied the efficiency of the extraction procedure, performed a cros s-reactivity study with different cortisol metabolites, and determined the reference values. Results: The assay shows within-run CVs varying from 1.6 to 5.3% and between-day CVs from 2.7 to 6.1% for urinary fre e cortisol concentrations from 58 to 1097 nmol/L. The assay demonstrat es an excellent linearity and a very good correlation with the Kallest ad Quanticoat Cortisol assay (slope = 0.94, y-intercept = 29 nmol/L, S y\x = 54 nmol/L, r = 0.996). The reference values were estimated at 42 -281 nmol/d. The extraction procedure shows an average recovery of 99. 0% and minimal interference with the cortisol metabolites tested with the exception of cortisone. Conclusions: The evaluation shows that the developed assay has the analytical characteristics required for its u tilization in a clinical laboratory.