Evaluation of a radioimmunoassay and establishment of a reference interval for salivary cortisol in healthy subjects in Denmark

Abstract

A commercial radioimmunoassay (RA) for salivary cortisol was evaluated using certified reference material in water and spiked to pooled saliva in the range 2.1-89.1 nmol/L. A variance component model for describing the effects of age, body mass index (BMI), diurnal variation, gender, days of sick leave during the past year, and smoking habits was established. Reference intervals for salivary cortisol in 120 healthy individuals performing their routine work were established according to the International Union of Pure and Applied Chemistry (IUPAC) and the International Federation of Clinical Chemistry (IFCC). The method evaluation of the certified reference material in water did not show any bias of the method, i.e. recovery was 97% [CI: 94%; 100.9%]. LOD (detection limit) was 1.59 nmol/L. The ratio between analytical and within-subject variation (CVa/CVi) was 0.14, indicating that the method was adequate for measurement in healthy subjects. Reference intervals were estimated to be from 3.6 to 35.1 nmol/L for samples at the time of awakening (05.27-07.27), 7.6-39.4 nmol/L for peak level in saliva samples collected 20 min after awakening (05.47-07.47), and LOD 10.3 nmol/L for late afternoon samples (17.00-19.00). Reactivity (increase from awakening to 20 min after awakening) was estimated to be 82% [CI: -179; 345%] and recovery (decrease from 20 min after awakening to 18.00) to be 80% [CI: 51; 109%]. Eighteen percent of the subjects showed a decrease in cortisol in saliva from awakening to 20 min after awakening. Salivary cortisol was not affected by age, body mass index, gender, smoking habits or days of sick leave during the past year.

Salivary cortisol and self-reported stress among persons with environmental annoyance

“…The similar cortisol concentrations and stable diurnal pattern across and within days agrees fairly well with the results from previous studies with normal participants and does not support the hypothesis of subnormal physiological stress functioning in the environmentally annoyed groups (27). This view was also corroborated by the fact that all of the groups showed a significant suppression of the HPA axis on the day after the ingestion of dexamethasone.…”

“…Westgard control charts were used to document that the analytical method remained under analytical and statistical control-in other words, that the trueness and the precision of the analytical methods remained stable. The performance of the methods has also been validated by participation in interlaboratory comparison schemes (26)(27)(28).…”

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

“…Salivary cortisol concentrations reflect unbound plasma cortisol concentrations and are therefore generally believed to be unaffected by variations in corticosteroid-binding globulin (CBG) concentrations (19). Indeed, we did not find statistically significant differences in late-night salivary cortisol concentrations for women taking hormonal contraceptive drugs compared to individuals not taking these drugs; women taking hormonal contraceptive drugs typically have high CBG concentrations (20).…”

Exhaustion measured by the SF-36 vitality scale is associated with a flattened diurnal cortisol profile

“…The method conductance has been validated in inter-laboratory comparison schemes. For detailed information on the laboratory analysis, see Hansen et al (2003;2006).…”