Establishment of reference intervals for the salivary cortisol circadian cycle, by electrochemiluminescence (ECLIA), in healthy adults

Publication date: Available online 19 February 2018
Source:Clinical Biochemistry
Author(s): Nadia Gagnon, Isabelle Fréchette, Pierre-Luc Mallet, Jean Dubé, Ghislaine Houde, Guy D. Fink
ObjectivesTo determine salivary cortisol reference intervals in a healthy adult population, at 6 different time points during a 24-hour (h) period.MethodsIn a prospective study, salivary cortisol concentrations were measured upon waking, one-hour post-waking and at specific times of the day: at 12 h00, 16 h00, 20 h00 and midnight. Samples were analyzed by the first and second-generation electrochemiluminescence assays (ECLIA) from Roche Cobas Cortisol®.ResultsSalivary cortisol values were obtained from 134 healthy volunteers. Reference intervals for the first-generation assay were 6.14–33.19 nmol/L (95% prediction interval) at waking, 5.42–28.06 nmol/L one-hour post-waking, 3.62–16.23 nmol/L at 12 h00, 2.78–15.27 nmol/L at 16 h00, 2.08–14.90 nmol/L at 20 h00 and 2.09–16.92 nmol/L at midnight. Mean salivary cortisol values were 14.63 nmol/L at waking and 6.44 nmol/L at midnight. Reference intervals for the second-generation assay were 1.50–22.02 nmol/L (2.5th to 97.5th percentiles) at waking, 1.50–20.87 nmol/L one-hour post-waking, 1.50–12.51 nmol/L at 12 h00, 1.50–13.03 nmol/L at 16 h00, 1.50–9.52 nmol/L at 20 h00 and 1.50–6.28 nmol/L at midnight. Values for the second-generation assay at all 6 different time points were almost half of the first-generation assay. The second-generation assay showed a better correlation with LC-MS/MS (r = 0,97).ConclusionOur study confirms that reference intervals for salivary cortisol are not comparable across first and second-generation Roche Cobas Cortisol® assays. Furthermore, the second-generation assay has a better correlation with LC-MS/MS and a better analytical performance (accuracy and precision).



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