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 (SAFdex and Fdex, 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, SAFdex significantly correlated with Fdex (r = 0·61, P < 0·0001). A cut‐off value of SAFdex > 2·0 nm and Fdex > 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 SAFdex seem to be good screening tools based on their noninvasive nature, remarkable reproducibility and diagnostic performances. Fil: Cardoso, Estela M. del Luján. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Médicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Arregger, Alejandro Luis. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Tumilasci, Omar Rene. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina Fil: Contreras, Liliana Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Médicas; Argentina
