Diagnostic accuracy of increased urinary cortisol/cortisone ratio to differentiate ACTH dependent Cushing's syndrome

Differential diagnosis between Cushing's Disease (CD) and Ectopic ACTH Syndrome (EAS) may be a pitfall for endocrinologists. The increasing use in clinical practice of chromatography and mass spectrometry improves the measurement of urinary free cortisol (UFF) and cortisone (UFE). We have recently observed that cortisol to cortisone ratio (FEr) was higher in a small series of EAS; in this paper we collected a larger number of ACTH-dependent CS to study the role of FEr to characterize the source of corticotropin secretion.