The diagnostic value of plasma adrenocorticotropic hormone (ACTH) to differentiate Adrenal Cushings syndrome from Cushings disease

Abstract

Introduction: Plasma adrenocorticotropic hormone (ACTH) level has been recommended as the first-step test to differentiate ACTH-independent Cushings syndrome (CS) from ACTH-dependent CS. When plasma ACTH values are inaccurate, the high-dose dexamethasone suppression tests (HDST) and serum dehydroepiandrosterone sulfate (DHEA-S) can be used to make the differential diagnosis of Cushings syndrome. The aim of this study was to assess the utility of plasma ACTH level in the differential diagnosis of CS and compare it with those of HDST and serum DHEA-S.

Methods: We conducted a retrospective and multicenter study from January 2000 to May 2012. A total of 92 patients with endogenous CS were included. Plasma ACTH, serum cortisol and 24 hour urine free cortisol (UFC) after HDST, and serum DHEA-S were measured.

Results: Fifty-seven patients had adrenal CS and 35 patients had Cushings disease. The area under the curve of plasma ACTH, serum DHEA-S and percentage suppression of serum cortisol and UFC after HDST were .954, .841, .950 and .997, respectively (all P <.001). The cut-off values for plasma ACTH, percentage suppression of serum cortisol and UFC after HDST were 24 pg/ml, 33.3%, and 61.6%. The sensitivity and specificity of plasma ACTH were 84.2%, 94.3% and those of serum cortisol and UFC after HDST were 95.8%, 90.6% and 97.9%, 96.7%, respectively. Conclusions: There was a significant overlap in plasma ACTH levels between patients with adrenal Cushings syndrome and those with Cushings disease. The HDST may be useful in differential diagnosis of Cushings syndrome, especially when plasma ACTH alone is not conclusive.