Cortisol assays across the physiologic spectrum: access immunoassay compared with LC-MS/MS

BACKGROUND: Immunoassays for cortisol are commonly used to evaluate adrenal function, but their similarity to gold-standard liquid chromatography-tandem mass spectrometry (LC-MS/MS) has not been demonstrated across the physiologic spectrum of cortisol production. METHODS: In this cross-sectional study, 97 adults without known adrenal disease underwent measurements of serum cortisol in the morning, post-dexamethasone suppression, and post-cosyntropin stimulation. Samples were analyzed on the Access Cortisol immunoassay and by LC-MS/MS. RESULTS: The assays showed good correlation across the physiologic spectrum, with close agreement at the lower end (mean bias -0.06 µg/dL [-1.7 nmol/L] post-dexamethasone suppression) and somewhat poorer agreement at the upper end of the physiologic spectrum (mean bias -1.68 µg/dL [-46.4 nmol/L] post-cosyntropin stimulation). Concordance using common interpretative cutoffs was good, with Cohen's κ = 0.93 for cortisol >10 µg/dL (275.9 nmol/L; morning), κ = 0.98 for cortisol 14.5 µg/dL (400 nmol/L; post-cosyntropin). CONCLUSIONS: Clinicians should be reassured that this immunoassay provides cortisol measurements similar to gold-standard LC-MS/MS across the physiologic continuum.