Adaptation of DELFIA cortisol kit for determination of salivary cortisol concentration

Salivary cortisol concentration seems to be an excellent indicator of the biologically active plasma cortisol level because of the nearly absence of corticoid-binding proteins in saliva. With regard to the easy, noninvasive, and stress-free nature of saliva sampling, this parameter greatly facilitates studies of the HPA (hypothalamus-pituitary-adrenocortical) axis, especially in children. A commercially available TR-FIA (time-resolved fluoroimmunoassay), the DELFIA (dissociation-enhanced lanthanide fluoroimmunoassay) method, proposed for plasma and urine cortisol analyses, was adapted for salivary cortisol measurement by means of simple modifications of the assay protocol. The sensitivity was determined to be 0.53 nmol/L. The intra- and interassay coefficients of variation ranged from 5.5 to 8.2 % and from 6.0 to 10.4 %, respectively. The present findings suggest that the DELFIA procedure provides a reliable, sensitive, and convenient alternative procedure to the assay for salivary cortisol.