Journal of endocrinological investigation
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J. Endocrinol. Invest. · Oct 1995
Comparative Study Clinical TrialMorning plasma free cortisol: inability to distinguish patients with mild Cushing syndrome from patients with pseudo-Cushing states.
Patients with Cushing syndrome have elevated 24 h urinary free cortisol excretion and loss of diurnal rhythm of plasma cortisol, however, morning total plasma cortisol concentrations are often similar to those of normal individuals. To test the hypothesis that an elevated morning plasma free cortisol could distinguish patients with Cushing syndrome from those without the disorder, we measured plasma free cortisol levels at 08:00 in 20 patients with surgically-confirmed mild Cushing syndrome, 19 patients with pseudo-Cushing states, and 9 normal volunteers. We then determined the sensitivity, specificity and diagnostic accuracy of plasma free cortisol for the diagnosis of hypercortisolism and for the diagnosis of Cushing syndrome. ⋯ However, there was considerable overlap of plasma free cortisol, plasma total cortisol and urinary free cortisol between the three groups precluding these tests alone from being useful to distinguish patients with mild Cushing syndrome from patients with pseudo-Cushing states. To achieve 100% sensitivity for the diagnosis of Cushing syndrome, the specificity for plasma free cortisol, plasma total cortisol and urinary free cortisol was 0.11, 0.32 and 0.32, respectively. We conclude that plasma free cortisol is of limited value in the differential diagnosis of hypercortisolism.