Endocrine Abstracts

Nocturnal salivary cortisol (NSC), urinary free cortisol (UFC) and overnight dexamethasone suppression testing (ODS) are recommended screening tests for Cushing’s syndrome (CS). Individual centers differ in their screening approach; UFC being the test of choice in Northern Ireland with ODS in patients with adrenal incidentalomas. NSC, which measures free cortisol, is not routinely used. The aims of this study were to 1. Evaluate the utility of NSC in the diagnosis of CS; and 2. Determine a NSC diagnostic threshold for CS. A retrospective study of all patients undergoing low dose dexamethasone suppression testing (LDDST) from 2010 to 2014 was performed. Patients were classified as ‘Cushing’s’ or ‘non-Cushing’s’ based on consultant clinical suspicion, biochemical results (UFC, ODS and LDDST) and clinical follow up. NSC samples, collected and stored over this time, were analysed using the ELISA technique. Diagnostic thresholds and test performance were determined using ROC curve analysis. Data was collected on 54 patients; 47 included in the study (20 Cushing’s; 27 non-Cushing’s). Seven patients were excluded (5 subclinical Cushing’s, 1 cyclical Cushing’s, 1 unclear diagnosis). NSC was the most effective diagnostic test for CS (AUC 0.928; P<0.001) with a threshold of 10 nmol/l having a sensitivity of 94.4%, specificity 88.5% and diagnostic accuracy of 90.9%. This was comparable to the LDDST (diagnostic accuracy 88.6%). UFC, and ODS (n=14; cut-off 50 nmol/l) were less effective with diagnostic accuracies of 72.3 and 42.9% respectively. In conclusion, NSC is an effective, easily performed screening test for CS, comparable to the LDDST and outperforming 24 h urinary collections.