Cortisol and behavior: 1. Adaptation of a radioimmunoassay kit for reliable and inexpensive salivary cortisol determination

The protocol presented in this paper allows for reliable salivary cortisol measures with a reduction of costs for analytical material to 25% compared to serum determinations.

Abstract

We adapted a commercial serum cortisol radioimmunoassay (RIA) kit for use with saliva specimen. Using 50 microliters sample volume, the lower sensitivity was found to be 0.02 microgram/dl with intraassay variation coefficients between 5.4 and 8.9% at different concentrations. The 50% intercept was either 0.5 or 0.26 microgram/dl (50 or 100 microliters standard/sample volume). Fifty-four early morning samples from healthy adults showed absolute concentrations which are closely comparable to respective data from other laboratories. A comparison of 35 saliva samples which were each assayed with the adapted RIA as well as with three other commercial kits revealed high correlations between these assays (r = .94 to r = .97). Data on salivary cortisol responses to CRH stimulation and dexamethasone suppression in healthy subjects further the validity of the assay results. The most important contribution of this assay modification, however, is thought to be its impact on analysis costs: The protocol presented in this paper allows for reliable salivary cortisol measures with a reduction of costs for analytical material to 25% compared to serum determinations.