Background: Immunoassay methods for urinary free cortisol (UFC) lack
specificity, and many procedures have not been fully evaluated for routine use. In
the current study we evaluated the Bayer ADVIA Centaur extraction UFC immunoassay and
compared results to those obtained by a specific gas chromatography-mass spectrometry
(GC-MS) method.
Results: The Bayer ADVIA Centaur cortisol assay lacked specificity.
Cortisone, a steroid present in urine at concentrations similar to those of cortisol,
demonstrated a cross-reactivity of 44%. In addition, the choice of matrix used to
resuspend steroids after solvent extraction from urine affected recovery. Recovery
was improved if the recommended urine reconstruction buffer was replaced by
steroid-free serum.
Conclusion: Irrespective of the sample matrix used, the Centaur method
overestimates UFC, giving results up to twice those obtained by a specific GC-MS
method.
