Day-to-day variation of late-night salivary cortisol in healthy voluntaries

ObjectivesThe study examines the components of biological variation of nocturnal salivary cortisol in healthy subjects.Design and methodsEight repetitive measurements were performed in seven subjects during a 25-day time period (study A), and then, for comparison, two salivary specimens were taken during two consecutive days from 20 subjects (study B). Salivary cortisol was measured with the Salimetrics HS-Cortisol assay.ResultsMean salivary cortisol (1.27 nmol/L), analytical variation (CVa = 15.4%), within-subject variation (CVi = 34.1%), between-subject variation (CVg = 35.3%), index of individuality (II = 1.06) and reference change value (RCV = 104%) were obtained for study A. Similar results were obtained from the set of samples of study B.ConclusionThe study results show a medium degree of individuality for salivary cortisol. Both conventional reference values and comparison of serial results may be equally used for clinical interpretation. A change greater of 104% between two successive measurements should be considered significant.