Supplementary Figure 1: Scatter graph of immunoassay (mAb) basal cortisol concentrations plotted against LC-MS/MS basal cortisol concentrations. The graph shows a strong positive correlation between the monoclonal antibody (mAb) immunoassay (Elecsys II) and LC-MS/MS-measured basal cortisol concentration. (p<0.0001, R2=0.5, Pearson r=0.7, 95% CI 0.5 – 0.7).Supplementary Figure 2: Morning basal cortisol concentrations as a predictor of LDSST outcomes by monoclonal antibody (mAb) immunoassay. The receiver-operating characteristic (ROC) curve with the true positive rate (sensitivity %) plotted against the false positive rate (100% - specificity%) for different cortisol threshold values for LDSST outcome. Adrenal insufficiency was determined as stimulated serum cortisol concentration <18.1 μg/dL (500 nmol/L) (A), <15.7 μg/dL (433 nmol/L) (B) and <12.6 (350 nmol/L) (C).Supplementary Figure 3: Morning basal cortisol concentrations as a predictor of LDSST outcomes by LC-MS/MS. The receiver-operating characteristic curve with the true positive rate (sensitivity%) was plotted against the false positive rate (100% - specificity%) for different cortisol threshold values for LDSST outcome. Adrenal insufficiency was determined as stimulated cortisol level <18.1 μg/dL (500 nmol/L) (A), <15.7 μg/dL (433 nmol/L) (B) and <12.6 (350 nmol/L) (C).