Measurement of late-night salivary cortisol with an automated immunoassay system

Abstract

Background: Measurement of late-night salivary cortisol concentrations is increasingly used as a screening test in suspected Cushing's syndrome. Cortisol concentrations are typically extremely low in latenight samples and discordant assay-specific reference ranges have been reported. Therefore, the aim of our study was to assess the analytical performance of the first automated cortisol immunoassay specified for salivary measurements and to establish late-night sampling reference-range data for this test. Methods: Salivary cortisol was measured using the Roche Cobas Cortisol assay (Roche Diagnostics). Five salivary pools in different concentration ranges were used to assess the inter-assay imprecision of this test in a two-centre evaluation protocol including two reagent lots. Linearity was tested by serial dilution. Salivary samples were obtained at 23:00 h from 100 apparently healthy volunteers using a commercially available salivary sampling device (Salivette, Sarstedt). A subset of 20 samples was used for method comparison with isotope dilution liquid chromatography-tandem mass spectrometry. Results: Inter-assay coefficients of variation (ns20) between 11.6% and 40.4% were found for mean cortisol concentrations between 12.9 and 2.6 nmol/L, with an estimated functional sensitivity of approximately 5.0 nmol/L. The test also gave linear results in the lowest concentration range between 1.0 and 8.3 nmol/L. Mean late-night salivary cortisol of 5.0 nmol/L was found for healthy individuals; the absolute range was 1.4-16.7 nmol/L, and the 95th percentile was 8.9 nmol/L. Substantially lower concentrations were found with isotope dilution LC-MS/MS compared to immunoassay results (mean concentrations 1.8 and 4.4 nmol/L, respectively). Conclusions: The automated assay investigated was found to offer acceptable analytical performance in the very low concentration range required for latenight salivary cortisol, despite a very short turnaround time. Using this assay, late-night salivary

Salivary cortisol as a diagnostic tool for Cushing's syndrome and adrenal insufficiency: improved screening by an automatic immunoassay

“…When comparing the results for late-night salivary cortisol with previous studies on this particular assay, our cutoff of 6.1 nmol/l was slightly lower than the 95th percentile of 8.9 nmol/l published by Vogeser et al (11). This difference may be explained by the fact that Vogeser et al exclusively investigated healthy control subjects, thereby providing an upper limit of normal instead of a ROC-generated cutoff.…”

Development and evaluation of a liquid chromatography tandem mass spectrometry method for simultaneous determination of salivary melatonin, cortisol and testosterone

“…Several procedures for quantification of salivary hormones by LC-MS/MS have been reported previously [27,28,[41][42][43][44][45][46]. Turpeinen et al proposed a simple liquid-liquid extraction (LLE) procedure where 0.1 mL saliva were extracted with dichloromethane and got a LOD for cortisol of 0.07 nmol/L [44].…”

Low levels of morning salivary α-amylase activity predict higher number of depressive symptoms in a community sample of children

“…Parents supervised the children in the collection and conservation of samples, which were immediately frozen at home at -20º C and picked up later that day. For free cortisol measurement, 500 l of saliva were taken for analysis using an automatized assay system (salivary cortisol on ROCHE Elecsys immunoassay system; see Chiu, Collier, Clark, &Wynn-Edwards, 2003, andVogeser, Durner, Seliger, &Auernhammer, 2006, for more details). This system does not require duplicate analysis of each saliva sample.…”