Fig. 1. Representation of the bias introduced by immunoassays in UFC measurements in 10 healthy control subjects and 10 patients with CS (unpublished data). UFC was simultaneously measured by an immunoassay, as described previously (Liaison, Diasorin, Italy), and GC-MS. The mean positive biases introduced by the immunoassay in all healthy control subjects and CS patients were determined to be 121% (range: 44–219%; N=33) and 135% (range: 33–344%; N=35), respectively.

Abbreviations: UFC, urinary free cortisol; CS, Cushing's syndrome; GC-MS, gas chromatography-mass spectrometry.