Direct time-resolved fluoroimmunoassay of serum and salivary cortisol

Because of the absence of cortisol-binding proteins in saliva, salivary cortisol concentration appears to be an excellent indicator of the biologically active plasma "free" cortisol concentration. Using a simple modifications of commercially available direct time-resolved fluoroimmunoassay (DELFIA) for serum cortisol (LKB-Wallac, 1244-003), authors obtained a sensitive and reliable analytical method for salivary cortisol determination. In a sample of healthy adults, there was a highly significant positive linear correlation between serum total and salivary cortisol concentrations (r = 0.834, p < 0.01) in time-matched samples. With regard to the easy, non-invasive and stress-free nature of saliva sampling and sophisticated method for salivary cortisol levels determination, this could greatly facilitate multiple sampling procedures and permit studies of hypothalamic-pituitary-adrenal axis, especially in children.