Cortisol Measurements in Cushing’s Syndrome: Immunoassay or Mass Spectrometry?

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.

Prospective Evaluation of Late-Night Salivary Cortisol and Cortisone by EIA and LC-MS/MS in Suspected Cushing Syndrome

“…Of course, many nonneoplastic forms of hypercortisolism, such as chronic kidney disease stage 5 and alcohol abuse disorder may also be associated with elevations of LNSC [ 61 , 77 ]. Usage of different reference ranges may also cause confusion [ 28 , 29 ]. Despite the many false positive EIA-F measurements, the near absence of any false negative results makes it a valuable screening test for the initial evaluation of patients suspected of ACTH-dependent CS.…”

“…A commonly used cortisol enzyme immunoassay (EIA-F) is inexpensive, Food and Drug Administration (FDA)-cleared, available internationally, and readily performed in clinical laboratories [ 26 , 27 ]. Furthermore, high-throughput platform cortisol immunoassay systems are widely available at reference laboratories around the world, although there are significant differences in their performance and reference ranges [ 28 , 29 ].…”

Dried urine and salivary profiling for complete assessment of cortisol and cortisol metabolites

“…Assessing HPA axis activity is most often accomplished by measuring cortisol levels. Cortisol concentrations can be measured in serum, plasma, saliva, urine and hair [1] , [2] , [3] . Although cortisol levels are necessary for evaluating HPA axis function, they may not be sufficient in all clinical scenarios.…”

Salivary cortisol in healthy dogs: a randomized cross-over study to evaluate different saliva stimulation methods and their effects on saliva volume and cortisol concentration

“…In our study we used LC-MS/MS to determine cortisol concentrations, in contrast to the commonly used immunoassays. Steroid measurements by LC-MS/MS does not rely on antigen binding and is less influenced by sample properties [ 24 , 25 ].…”