Radioimmunoassay of salivary oestriol: Application to the assessment of foetal well-being

A simple, rapid radioimmunoassay for salivary oestriol has been developed based upon a radioiodinated tracer and a Sepharose-coupled antiserum with high specificity for oestriol and oestriol-3-conjugates. The standard curve covers the range 0.75 to 17.5 nmol/L, and assay sensitivity and precision are adequate for determination of third trimester oestriol concentrations. This assay, with a short incubation time (15 min) and a high tracer activity, has proved suitable for automation using a continuous-flow system based upon the 'Southmead System' described by Ismail and co-workers. Preliminary ether extraction is unnecessary since salivary oestriol is predominantly in the unconjugated form. Measurements of unconjugated oestriol in matched samples of plasma and saliva show an excellent correlation (r=0.95). A preliminary study has been carried out to assess the feasibility of constructing individual daily salivary oestriol profiles throughout the third trimester. Data have now been collected on normal, diabetic and other high-risk patients, and these indicate that salivary oestriol measurements provide a practical alternative to the determination of plasma unconjugated oestriol. (author)