Measurement by radioimmunoassay of unconjugated estriol in pregnancy serum.

Antisera to estriol 6--onjugates were tested for suitability in the direct radioimmunoassay of unconjugated estriol in extracts of pregnancy serum. Assessment of specificity through titration with competing steroids allowed a selection to be made within the group of antisera. The measurement was then standardized by checking the absence of analytical blank (solvent and sample blank) and the extent of binding variability associated with the use of charcoal-dextran as a separating agent. Validation was made by means of the usual recovery and dilution tests, and by a cross-comparison of analytical data obtained with different antisera; reproducibility of calibration curve and within-and between-assay variability was evaluated under routine conditions. The validity of the clinical information was assessed by assaying 202 samples randomly collected throughout normal pregnancy from the 16th week to term: both trend and levels of unconjugated estriol concentration were found to be in good agreement with the literature data.