Diagnostic value of salivary cortisol in Cushing's syndrome (CS)

Objective The diagnosis of Cushing's syndrome (CS) remains a challenge in clinical endocrinology. The aim of this study was to determine the reproducibility and diagnostic value of late‐night salivary cortisol (SAF₂₃) for CS and its utility along the follow‐up of treated patients. In addition, using the same radioimmunoassay reactives, the cut‐off values for saliva and serum cortisol, assessed synchronically after the overnight 1 mg dexamethasone suppression test (DST), were defined. Design Twenty‐one patients with confirmed CS and 121 volunteers were studied. All the subjects collected 24‐h urine for cortisol (UFC). On the same day whole saliva was obtained from the subjects at 23 h for SAF₂₃. The intraclass coefficient of correlation (ICC) of SAF₂₃ was estimated in 47 subjects (21 CS and 26 C). At 8 h, after DST, simultaneous saliva and serum samples for cortisol (SAF_dex and F_dex, respectively) were obtained in 51 subjects (17 CS and 34 C). After specific therapy, 18 patients with CS were followed with SAF₂₃ measurements. SAF and F were expressed as nm . Results The intraclass coefficient of correlation of SAF₂₃ was 0·89 in CS and 0·83 in C. SAF₂₃ > 3·8 nm showed a sensitivity and specificity of 100% and 97·5%, respectively, for diagnosing CS. SAF₂₃ correlated positively with UFC (r = 0·685; P = 0·0001). After DST, SAF_dex significantly correlated with F_dex (r = 0·61, P < 0·0001). A cut‐off value of SAF_dex > 2·0 nm and F_dex > 50·0 nm detected CS with 100% sensitivity and specificity. After successful surgical therapy, 13 patients with CS had SAF₂₃ levels < 3·8 nm (1·4 ± 0·8 nm ). Conclusions SAF₂₃ and SAF_dex seem to be good screening tools based on their noninvasive nature, remarkable reproducibility and diagnostic performances.