Polarisation fluoroimmunoassay of serum and salivary cortisol

Polarisation fluoroimmunoassays for serum and salivary cortisol were developed using the steroid labelled at the 3-position with fluorescein and antiserum raised in sheep. To avoid interfering factors present in the biological fluids, cortisol was extracted with dichloromethane prior to assay, which was then accomplished without the need for any further separation or blank-correction procedures. The methods were sufficiently sensitive to cover the normal morning ranges for serum and salivary cortisol and correlated acceptably with established fluorimetric and radioimmunoassay techniques. The salivary cortisol assay was more precise than the serum assay, reflecting the greater case with which cortisol may be extracted from saliva. The potential usefulness of salivary cortisol assays was illustrated by a preliminary study showing that the circadian variation in three children was similar to that in an adult.