Urinary free cortisol: An automated immunoassay without extraction for diagnosis of Cushing's syndrome and follow-up of patients treated by anticortisolic drugs

The 24-hour urinary free cortisol (UFC) is a recommended test for the diagnosis and follow-up of patients with Cushingu0027s syndrome (1). Analytical difficulties encountered in UFC determination are well-documented, especially concerning patients treated with anticortisolic drugs due to potential cross-reactivity with cortisol precursors and metabolites (2). This interference is often described in immunoassay (IA). Nowadays, the alternative technique is the commonly considered "gold standard": liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). However, the routine use of LC-MS/MS raises other challenges: it requires expensive equipment and skilled staff.