MON-272 Evaluation of Cortisol Assay Measurements across the Physiologic Spectrum: Mass Spectrometry versus Modern Immunoassay

Abstract Disclosure: A.J. Newman: None. S. Mahrokhian: None. J. Chan: None. I. Hanna: None. A. Ferrebus: None. J.M. Brown: None. R.J. Auchus: None. A. Vaidya: None. Background: Accurate and specific assays for serum cortisol are essential to the clinical endocrinologist. However, the availability of cortisol assays varies across laboratories. We evaluated the correlation of serum cortisol measurements by liquid chromatography tandem mass spectroscopy (LC-MS/MS) with a modern cortisol immunoassay (IA) across the physiologic range of cortisol production in healthy participants. Methods: Healthy adults (n=97), without known or suspected cortisol excess or insufficiency, and who were not taking glucocorticoid medications, were prospectively recruited to undergo measurement of morning serum cortisol, post-overnight dexamethasone (1 mg) suppression testing (DST), and a 250 mcg cosyntropin stimulation (CST). Serum cortisol was measured by LC-MS/MS and with the Beckman-Coulter Access cortisol polyclonal IA. Inter-assay cortisol concentrations were evaluated using correlation analyses and Bland-Altman plots. Results: Median random morning cortisol by IA was 8.5 mcg/dL (IQR 6.8-11.5) and by LC-MS/MS was 8.7 mcg/dL (7.0-11.7). After 1 mg DST, median cortisol by IA was 0.8 mcg/dL (0.6-1.1) and by LC-MS/MS was 0.8 mcg/dL (0.6-1.2). Following CST, median cortisol by IA was 19.8 mcg/dL (17.4 - 22.1) and by LC-MS/MS was 20.9 mcg/dL (17.8-24.0). The correlation between LC-MS/MS and IA serum cortisol concentrations across the entire range was strong (r = 0.95, P < 0.001). In the range relevant to the evaluation for adrenal insufficiency, where cortisol < 5 mcg/dL, measured values were highly correlated (r = 0.77, P < 0.001). Similarly, in the range of values typically used to adjudicate a normal hypothalamic-pituitary-adrenal axis (10 - 20 mcg/dL), values were again highly correlated (r = 0.76, P < 0.001). CONCLUSIONS: Cortisol measured by the widely used Access immunoassay was highly correlated with the gold standard of LC-MS/MS across the physiologic range of cortisol production, including morning values, post-dexamethasone suppressed values, and post-cosyntropin stimulated values. These findings provide reassurance that the use of this specific Access IA serves as a reliable surrogate for the gold standard LC-MS/MS when evaluating cortisol across the spectrum of adrenal function. Presentation: Monday, July 14, 2025