Measurement of late-night salivary cortisol with an automated immunoassay system
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Michael Vogeser
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 late-night 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 23:00h 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 (n=20) between 11.6% and 40.4% were found for mean cortisol concentrations between 12.9 and 2.6nmol/L, with an estimated functional sensitivity of approximately 5.0nmol/L. The test also gave linear results in the lowest concentration range between 1.0 and 8.3nmol/L. Mean late-night salivary cortisol of 5.0nmol/L was found for healthy individuals; the absolute range was 1.4–16.7nmol/L, and the 95th percentile was 8.9nmol/L. Substantially lower concentrations were found with isotope dilution LC-MS/MS compared to immunoassay results (mean concentrations 1.8 and 4.4nmol/L, respectively).
Conclusions: The automated assay investigated was found to offer acceptable analytical performance in the very low concentration range required for late-night salivary cortisol, despite a very short turn-around time. Using this assay, late-night salivary cortisol concentrations below 8.9nmol/L are typically found in healthy volunteers.
Clin Chem Lab Med 2006;44:1441–5.
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©2006 by Walter de Gruyter Berlin New York
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- National survey on the pre-analytical variability in a representative cohort of Italian laboratories
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Articles in the same Issue
- Initiation and progression of atherosclerosis – enzymatic or oxidative modification of low-density lipoprotein?
- Blood transfusions in athletes. Old dogmas, new tricks
- Molecular detection of tyrosinase transcripts in peripheral blood from patients with malignant melanoma: correlation of PCR sensitivity threshold with clinical and pathologic disease characteristics
- Increase in and clearance of cell-free plasma DNA in hemodialysis quantified by real-time PCR
- Lipoprotein lipase gene polymorphism at the PvuII locus and serum lipid levels in Guangxi Hei Yi Zhuang and Han populations
- Interpretation of cardiac troponin T behaviour in size-exclusion chromatography
- Point-of-care C-reactive protein testing in febrile children in general practice
- Improvement in HPLC separation of porphyrin isomers and application to biochemical diagnosis of porphyrias
- Measurement of late-night salivary cortisol with an automated immunoassay system
- Combining markers of nephrotoxicity and hepatotoxicity for improved monitoring and detection of chronic alcohol abuse
- Stone or stricture as a cause of extrahepatic cholestasis – do liver function tests predict the diagnosis?
- Insulin resistance and enhanced protein glycation in men with prehypertension
- Prevalence-dependent decision limits for the early detection of type 2 diabetes mellitus in venous blood, venous plasma and capillary blood during glucose challenge
- Analytical performance and clinical utility of the INNOTEST® PHOSPHO-TAU(181P) assay for discrimination between Alzheimer's disease and dementia with Lewy bodies
- Variations in assay protocol for the Dako cystatin C method may change patient results by 50% without changing the results for controls
- Approved IFCC recommendation on reporting results for blood glucose: International Federation of Clinical Chemistry and Laboratory Medicine Scientific Division, Working Group on Selective Electrodes and Point-of-Care Testing (IFCC-SD-WG-SEPOCT)
- National survey on the pre-analytical variability in a representative cohort of Italian laboratories
- 10% CV concentration for the fourth generation Roche cardiac troponin T assay derived from Internal Quality Control data
- Biological variation of non-SI traceable biological quantities: example of proteins
- Effect of tibolone therapy on lipids and coagulation indices
- Acknowledgement
- Contents Volume 44, 2006
- Author Index
- Subject Index
