SAT-390 New Cortisol Threshold for Diagnosis of Adrenal Insufficiency After Cosyntropin Stimulation Testing Using the Elecsys Cortisol II, Access Cortisol, and LC-MS/MS Assays

The peak cortisol response 30 or 60 minutes after cosyntropin [ACTH (1-24)] is regarded to be ≥18 μg/dL (500 nmol/L). This threshold is based on older immunoassays using polyclonal antibodies to detect cortisol. The use of more specific monoclonal antibody immunoassays or LC-MS/MS has been reported to provide a lower cutoff for a normal response. We compared the polyclonal antibody cortisol assay, Elecsys Cortisol I (Roche Diagnostic), whose peak cortisol response to ACTH 250 μg is ≥18 μg/dL (500 nmol/L), to two monoclonal antibody cortisol assays, Elecsys Cortisol II (Roche Diagnostic) and Access Cortisol (Beckman-Coulter), and LC-MS/MS in 55 patients undergoing testing for possible adrenal insufficiency. Using the Elecsys Cortisol I assay as the gold standard, all but 11 patients had a normal response at 30 or 60 minutes. Those patients were felt to have secondary adrenal insufficiency due to exogenous glucocorticoid therapy, endogenous glucocorticoid exposure, pituitary surgery, critical illness, or opioid use. ROC curves were used to determine thresholds for the other assays. A cortisol threshold of 14.5 μg/dL (400 nmol/L) would result in sensitivities and specificities of 100% and 94% for the Elecsys Cortisol II assay, 100% and 100% for the Access Cortisol assay, and 100% and 88% for LC-MS/MS. In conclusion, we recommend a new peak cortisol threshold of 14.5 μg/dL (400 nmol/L) after ACTH stimulation testing using one of these more highly specific cortisol assays. It will be important for clinicians to be aware of this new cutoff when evaluating patients for adrenal insufficiency.