Exp Clin Endocrinol Diabetes 2007; 115 - P02_050
DOI: 10.1055/s-2007-972457

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

M Vogeser 1, E Seliger 2, J Durner 1, C Auernhammer 3
  • 1Klinikum der Universität München, Institut für Klinische Chemie, München, Germany
  • 2Klinikum der Martin Luther Universität Halle, Klinik für Gynäkologie und Reproduktionsmedizin, Halle, Germany
  • 3Klinikum der Universität München, Medizinische Klinik 2, München, Germany

Objective: 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 which is 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, Mannheim, Germany). Five salivary pools in different concentration ranges were used to assess the inter-assay imprecision of this test applying a bi-centrical evaluation protocol including two reagent lots. 2300-h salivary samples were obtained 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 2.6 nmol/L, with an estimated functional sensitivity of approx. 5.0 nmol/L. A mean late-night salivary cortisol of 5.0 nmol/L was found in healthy individuals, the absolute range was from 1.4 to 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 4.4 nmol/L, and 1.8 nmol/L, respectively).

Conclusion: The automated assay investigated was found to offer acceptable analytical performance also in the very low concentration range of late-night salivary cortisol despite a very short turn-around time. Using this assay, late-night salivary cortisol concentations below 8.9 nmol/L are typically found in healthy individuals.