The Performance and Reproducibility of Late-Night Salivary Cortisol Estimation by Enzyme Immunoassay for Screening Cushing Disease

Objective: Our study aimed to establish a local reference range for late-night salivary cortisol (LNSC) using enzyme immunoassay (EIA) and to study the intra-individual reproducibility of LNSC.Methods: Prospective study involving 30 healthy subjects (HS) with body mass index (BMI) 25 kg/m2 and 28 patients with Cushing disease (CD). Salivary sampling was performed on 2 consecutive nights and assayed by EIA. The reference range was established using LNSC values of HS, and receiver operating characteristic (ROC) curves were used to determine diagnostic cutoffs.Results: The mean LNSC level of CD was significantly higher than HS and OS (CD: 16.96 ± 9.11nmol/L, HS: 1.30 ± 0.95 nmol/L, and OS 1.21 ± 0.78 nmol/L). A cutoff of 2.92 nmol/L differentiated CD from HS with 100% sensitivity and 96.7 % specificity, and a cutoff of 5.04 nmol/L yielded a specificity of 100% with a sensitivity of 96.4% to distinguish CD from OS. There was more intra-individual variabil...