Direct chemiluminescence immunoassay of estradiol in saliva

A sensitive and simple direct solid-phase chemiluminescence immunoassay is described for estradiol in saliva. In this assay, a second antibody is bound to the wells of microtiter plates. Either buffer with standards or saliva (100 microL) is incubated in these wells with monoclonal anti-estradiol antibody and with estradiol-isoluminol conjugate. Incubation time is 2 h. Chemiluminescence of the bound fraction is measured in a manually operated luminometer (Biocounter). The assay has a detection limit of 3.8 pmol/L; analytical recovery of added estradiol is 96.8% (SD 7.0%); within- and between-assay CVs range between 2.5% and 12.7%. Forty unknown saliva samples can be assayed and results calculated within 4.5 h. Results of a slightly modified procedure-with black microtiter plates and a prototype of an automated plate reader (Luminoskan)--compare well with those of the described method (r = 0.97). Because steroid-binding globulins have been found in saliva, the effect of displacing agents on the results of the direct chemiluminescence assay is described.