Clinical accuracy of midnight salivary cortisol measured by automated electrochemiluminescence immunoassay method in Cushing's syndrome

BackgroundThe diagnosis of Cushing's syndrome (CS) represents a challenge for endocrinologists. Several screening tests are used, but none of them seems to be the gold standard for the diagnosis. The aim of this study was to confirm the diagnostic value of salivary cortisol (SC) as a first-level screening test and to evaluate the clinical performance of a electrochemiluminescence immunoassay (ECLIA) method.MethodsIn 33 patients with a strong clinical suspicion of CS, we evaluated urinary free cortisol, circadian rhythm plasma cortisol (PC) and morning PC after low-dose dexamethasone suppression test (LDDST). At the same sampling times, we evaluated SC analysed by the same automated method. Correlation studies were evaluated by Spearman index (significance P < 0.05).ResultsOn the basis of biochemical results CS was confirmed in 21/33. SC was significantly correlated to PC at 12:00 and 23:00. Thus, we chose 8.3 nmol/L as midnight SC cut-off value with 100% sensitivity and 97.4% specificity. The cut-off chos...