Use of salivary cortisol measurements in young infants: a note of caution.

In order to investigate possible contamination of saliva samples with formula or breast milk obtained from young infants for cortisol assays, we measured cortisol concentrations in 3 common infant milk formulas and in breast milk before and after defatting and extraction using a commercial radioimmunoassay kit. Cortisol concentrations obtained prior to defatting and extraction were equal to or higher than (1.64-82.80 micrograms/dL) levels reported for salivary cortisol levels reported in newborn infants (0.09-2.08 micrograms/dL). Cortisol concentrations obtained after the defatting and extraction were lower (0.02-0.15 micrograms/dL), indicating that values obtained prior to defatting and extraction were due to cross-reacting substances as well as cortisol. As saliva samples are not routinely defatted or extracted prior to being assayed, high cortisol levels and interfering substances in formula and breast milk could contaminate salivary cortisol measurements in young infants. The present study suggests that appropriate controls should be taken when making salivary cortisol measurements in young infants to help ensure accurate results.