Radioimmunoassay of cortisol in saliva

A direct (without extraction) radioimmunoassay of cortisol in saliva has been developed. The samples of saliva were subjected to four freezing-thawing cycles in order to decrease viscosity which may interfere with the determination. The method is simple, has good specificity and reproducibility. The determination in saliva has also the merit of noninvasiveness, and besides, the level of cortisol in saliva reflects the free, biologically active fraction of the hormone in blood serum. The volume of saliva required does not exceed 25 microliters per tube and the range of concentrations is between 0.6 and 15 nanograms per milliliter (1.5-40 nmol/l).