Effect of salivary proteins on binding curves of three radioimmunoassay kits: Amerlex-M progesterone, Amerlex cortisol, and Biodata testosterone

Abstract

Radioimmunoassay (RIA) is generally used to measure certain salivary hormones because of its high sensitivity. For speed and simplicity, it has been used in the form of 'direct' assays, i.e., without first extracting the analyte from its matrix. Investigating the effect of the principal salivary proteins on the binding behavior of three commercial RIA kits, we found that the Amerlex-M [125I]progesterone binding was greatly reduced when α-amylase and mucins were added to the binding medium, whereas IgA and IgG were less effective. The Serono Biodata [125I]testosterone binding was unaffected by proteins, while the Amerlex [125I]cortisol binding was decreased by α-amylase and mucins. The protein influence was largely eliminated when an extraction step was incorporated. Thus, direct RIA of saliva may be subject to matrix effects, to extents that vary with the kit and that may adversely affect the quality of the assay results.