Ann Lab Med 2020; 40(4): 285-296  https://doi.org/10.3343/alm.2020.40.4.285
Cortisol Measurements in Cushing’s Syndrome: Immunoassay or Mass Spectrometry?
Gregori Casals, M.D., Ph.D.1,2,3 and Felicia Alexandra Hanzu , M.D., Ph.D.2,4,5
1Department of Biochemistry and Molecular Genetics, Hospital Clínic, Barcelona, Spain; 2Institut d’Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain; 3Centrode Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (CIBERehd), ISCIII, Madrid, Spain; 4Department of Endocrinology and Nutrition, Hospital Clínic, Barcelona, Spain; 5Department of Medicine, Faculty of Medicine and Health Sciences, University of Barcelona, Barcelona, Spain
Corresponding author: Gregori Casals, M.D., Ph.D.
Department of Biochemistry and Molecular Genetics, Hospital Clínic Universitari, Villarroel 170, Barcelona 08036, Spain
Tel: +(3493)2275400 × 2667 Fax: +(3493)2275697 E-mail: casals@clinic.cat
Received: November 8, 2019; Revised: December 20, 2019; Accepted: February 7, 2020; Published online: July 1, 2020.
© Korean Society for Laboratory Medicine. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Determination of cortisol levels in the urine (24 hours urine free cortisol), saliva (late-night), or serum (total cortisol after dexamethasone suppression) is recommended to screen for Cushing’s syndrome (CS). This review focuses on the differences between the frequently used cortisol-antibody immunoassay-based methods and the highly specific mass-spectrometry-based methods that are progressively being employed in clinical laboratories for CS screening. The particular characteristics of cortisol metabolism and the lack of specificity of the immunoassays cause marked differences between both methods that are in turn highly dependent on the biological matrix, in which the cortisol is measured. Understanding the origin of these differences is essential for the interpretation of these results. Although cross-reactivity with endogenous steroids leads to grossly inaccurate results of immunoassay measurements of cortisol in the saliva and urine, preliminary evidence suggests that the clinical sensitivity of CS screening using immunoassays may be similar to CS screening using mass spectrometry. However, mass spectrometry offers more accurate results and considerably reduced variation across laboratories, while avoiding false-positive results. Moreover, mass spectrometry can overcome some common diagnostic challenges, such as identification of exogenous corticosteroids or simultaneous assessment of appropriate dexamethasone levels in suppression tests. Further, comprehensive mass spectrometry-based profiling of several steroid metabolites may be useful for discriminating among different subtypes of CS. Finally, this review discusses the main preanalytical factors that could cause variations in cortisol measurements and their influence on the reliability of the results.
Keywords: Cortisol, Immunoassay, Mass spectrometry, Sensitivity



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