Specificity assessment of immunoassay kits for determination of urinary free cortisol concentrations.

Background: In immunoassay kits for determination of urinary free cortisol (UFC) concentrations, the results vary markedly from kit to kit, so we compared in this study the reaction specificity among 4 commercially available immunoassay kits to determine the applicability of these assays in routine determination of UFC concentrations.

Method: Using 4 commercially available kits, cross-reaction was investigated. In addition, urine samples were fractionated by HPLC to investigate endogenous immunoreactive cortisol responses.