Endocrine Abstracts

Introduction: Home cortisol testing in saliva is simple and cheap. Late-night salivary cortisol or cortisone and waking salivary cortisone show high diagnostic accuracy for Cushing’s syndrome and adrenal insufficiency, respectively. This project aimed to develop a Liquid Chromatography-Tandem mass Spectrometry (LC-MS/MS) method to measure cortisol and cortisone in saliva in an NHS teaching hospital, which offers an accurate alternative for measurement of cortisol and cortisone that overcomes any assay interference issues in immunoassays.

Methods: Samples were collected using Salivette® devices. The method was developed using Chromsystems® - MassChrom® Cortisol, Cortisone in Saliva. Analysis was performed using LC-MS/MS.

Results: Validation of the assay revealed no significant effects from ion suppression or carryover. Lower limit of detection and quantitation were 0.77 and 1.40 nmol/l for cortisol, and 1.07 and 2.13 nmol/l for cortisone, respectively. The assay was linear from 2.83 to 267.04 nmol/l for cortisol and 25.96 to 506.75 nmol/l for cortisone, with r²>0.999. Intra-assay precision was < 5% CV for cortisol and cortisone and inter-assay precision <10% across the analytical range of the assay. Uncertainty of Measurement was <10%. An assessment of bias for cortisol was performed by comparison to external quality control reference values, with all results falling within the interquartile range of the target reference values. Patient comparison (n = 50) gave regression equations using Passing-Bablok for cortisol and cortisone of y=0.01919+0.9649x and y=0.6382+0.9536x, both with r²=0.99 (CI of 95%). The mean relative differences were 2.1% for cortisol and 2.6% for cortisone between methods.

Conclusion: We have developed an assay for the measurement of salivary cortisone and cortisol. The test will obviate the need to send samples to an external central laboratory, hence improving turnaround time and reducing costs. The validation and verification processes demonstrated that the assay is accurate and precise and suitable for routine clinical application.