A new chemiluminescence immunoassay for the determination of serum, plasma, urine and saliva cortisol on the IDS-iSYS Automated System

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 41-52-HPA Axis & Disease States
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-51
Chris Martin Roffe*1, Philipp Grimminger2, Craig Ramsey1, Zoltan Seres1 and Martin Bidlingmaier3
1Immunodiagnostic Systems Ltd, United Kingdom, 2Medizinische Klinik und Poliklinik IV, Klinikum der Universitaet, Munich, Germany, 3Klinikum der Universitaet, Munich, Germany
Background: Abnormal changes in cortisol levels due to hypothalamic, pituitary or adrenal malfunction, such as in Cushing’s syndrome and Addison’s disease, can lead to severe metabolic imbalance. Current diagnostic guidelines recommend the measurement of cortisol in blood following stimulation or suppression stress tests, but also the measurement of integrated 24hour cortisol secretion in urine or of late night salivary cortisol.. We present here the development of a competitive immunoassay for the measurement of cortisol,,on a chemiluminescence analyzer (IDS-iSYS). 

Method: Cortisol in the sample competes with biotinylated cortisol for binding to a monoclonal anti-cortisol-acridinium conjugate in a first incubation. Streptavidin-coupled magnetic particles are added and after further incubation and washing, the bound anti-cortisol-acridinium is measured whereby chemiluminescence generated is inversely proportional to the cortisol concentration in the sample. Total time to first result is 8 minutes.  IDS-iSYS assay results were correlated against commercially available assays for serum (Roche, Cobas), urine and saliva (IBL, EIA).

Results: The assay range covering all matrices was determined at 0.05-75µg/dL with an analytical sensitivity of 0.02ug/dL. Inter-assay precision CVs were between  3.6% - 8.9% at concentrations 0.5 to 54µg/dL. For the same samples intra-assay precisions were between 2.9% - 5.9%. The assay showed linearity between 86-103% at 0.2µg/dL to 48.4µg/dL Matched serum and plasma samples were run on the IDS-iSYS showing excellent correlation (plasma = 0.92x serum + 0.95, R2=0.95, n=35). In serum samples from two external quality assessment schemes, UK NEQAS and the German DGKL, the iSYS showed excellent correlation to the Roche assay (y=0.98x + 1.69, R2=0.99, n=15; and y=0.90x + 1.86, R2=0.96, n=15). Additionally the iSYS had excellent agreement to the target gold standard mass spectrometry values of the DGKL samples (y=1.02x + 16.41, R2=0.99). Good correlation to the IBL assays was observed with urine and saliva samples (y=0.92x + 1.34, R2=0.95, n=10; and y=0.90x + 0.09, R2=0.97, n=28).

 Conclusion: The data presented above demonstrate that the fully automated IDS-iSYS cortisol assay potentially presents a new, accurate and reliable immunoassay for all commonly used sample types across a wide assay range. The extremely short time to first result makes the assay suitable also for use during diagnostic procedures like adrenal vein sampling.

Disclosure: CMR: Employee, Immuno Diagnostic Systems Ltd. PG: Employee, Immuno diagnostic Systems Ltd. CR: Employee, Immuno Diagnostic Systems Ltd. ZS: Employee, Immuno Diagnostic Systems Ltd. MB: Consultant, Immunodiagnostic Systems Ltd.

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm